So far, the summer hasn't disappointed. It's been blazingly hot, there's been the usual selection of moment-defining musical acts and sun-soaked festivals encapsulating the joys of the season, the kind of sumptuously vivid scenes you'd expect to see in a Wes Anderson movie. Britain has sweltered. So sad to experience, then, the cold shower that was this year's Man Booker prize longlist announcement, normally a staple in my summer diet of heady discovery. It's the time of year when young writers wait eagerly to discover exciting new voices from all over the world and you're angling your head on hot trains to see who's reading what and jostling uncomfortably close to other commuters. Such a pity that this year's list has cast such a cloud

The Booker longlist is certainly representative of the prize's new global reach, comprising six UK authors, four from the US, an Australian and two from Ireland. I have to say my reaction to the announcement was lukewarm. It feels rather lacklustre in comparison to the vibrancy and diversity of last year's longlist, which saw New Zealand's Eleanor Catton, the youngest ever winner, scoop the prize from a group that included two first-time authors, Catton and the dazzling NoViolet Bulawayo. Where are the stories of this year's list? Those interesting personal angles that make you want to rush out and purchase the books? Last year, I jotted down several that had me almost salivating at the prospect of buying them.

The 2014 longlist seems too much like what we have come to expect from prize announcements, very white and predominantly male. There have been a few raised eyebrows at the exclusion of some high-profile names, notably the brilliant Donna Tartt and the likes of Martin Amis, but it's even more jarring that of the 13, there are barely any writers of colour – in fact only Indian British author Neel Mukherjee makes the cut with his novel, The Lives of Others.

Really? Just one non-white author? It's disheartening that the Booker has once again chosen to ignore the talents of writers of colour, who look to these lists for inspiration, to see themselves reflected and to unearth their literary icons. Once again, it feels like if you're not white and male, your talents don't matter. There are only three women, and in an unfortunate turn of events, most writers from the Commonwealth have been sidelined in favour of their US counterparts. This year the Booker was opened up to US authors, after 45 years of recognising only the work of writers from UK, Ireland and Commonwealth countries, and the lack of diversity, including the paltry number of women, is alarming. I wonder at this constant reluctance to fully and fairly acknowledge our female authors; this fear of giving women the plaudits they deserve in a largely patriarchal hierarchy is deeply embedded in our society. So much so that it's necessary to have prizes specifically for women. Why must publishing continue to move at a tortoise-like pace when it comes to tackling diversity? It's just more of the same.

What of the inclusion of more authors from independent publishing houses? There's a welcome revival happening on the indie scene with literary platforms such as Brixton Bookjam, Black Book Swap and Words of Colour, as well as publishing houses And Other Stories, Galley Beggar Press, Jacaranda Books, and Unbound, whose author Paul Kingsnorth receives a Booker nod for The Wake. There is a wealth of voices out there. Where are the nods on this list for the likes of Bernardine Evaristo and Kamila Shamsie?

I have to say, looking at the Booker judging panel, it makes sense. I'm sure they're perfectly cultured, discerning people but there isn't one judge of colour, male or female. I find it disheartening that nobody actually stops to consider that it looks archaic and dull. Why not show the vibrancy of our arts world? This should be depicted both on the judging panel and the book list. There are plenty of writers who would be happy to be selected as judges for a Booker. And of course, books selected are reflective of the tastes of the judges.

If the panel was more diverse, then perhaps the list would be more inclusive. Here's a radical idea – next time, perhaps the panel could be made up of an equal number of men and women as well as a few non-white people.

One of the strengths of the Booker prior to its international revamp was that it showcased writers from the Commonwealth, introducing these authors to new and larger audiences, much like the Caine prize. This is also the aim of the SI Leeds literary prize, a new national, biennial UK prize for female writers of colour. This year's Booker longlist has only one non-British writer from the Commonwealth, Australia's Richard Flanagan, nominated for The Narrow Road to the Deep North.

I wonder if this rather tactile and political list marks the sign of things to come, with each year even more US authors having a larger presence. And other than Britain, what will the Commonwealth representation be next year? We are all happy that the Commonwealth Games have arrived to capture our imagination but this is certainly not the case with the Booker. Commonwealth additions made the list more colourful and much more interesting.

That said, I'm pleased to see the inclusion of Ali Smith. After a hiatus, Smith is back with a flourish for her genre-bending new novel How to be Both, and David Mitchell has been longlisted for a third time, for The Bone Clocks. The Booker has a huge reach; it makes the careers of authors and in a world where books are continuously fighting for their place against other forms of entertainment the Booker should be showcasing a much more inclusive and diverse list with a wider appeal, not aiming to reach only white middle- to upper-class readers, and by default saying that only one type of audience matters.

The power of books is their ability to cut across all of the societal barriers, and authors from varied backgrounds should be given the opportunity to do so.

Each year, there's some surprise about the Booker's longlist announcement, with critics expressing shock at one element or another of the list. But last year the contest made strides. What a shame, then, that in its quest to become more global, it seems to have done the exact opposite.

Irenosen Okojie is a writer and arts project manager. She is the 2014 prize advocate for the SI Leeds literary prize. Her debut novel will be published by Jacaranda Books in 2015. @IrenosenOkojie