The short answer is racism.

The longer answer is Orientalism, a thought system first thoroughly discussed by Edward Said.

He defines Orientalism as "a style of thought based upon an ontological and epistemological distinction made between "the Orient" and (most of the time) "the Occident." p. 2. And this system is used for "dominating, restructuring, and having au­thority over the Orient." p.3

This little definition is packed with a lot and the chapter that follows contains even more. But for the sake of this question it is important to note that Orientalism is a thought system whereby a clear division is built between the West and East and that division is defined by the West with "non-western" sources to confirm "Western" ideas. It dominated, and some say continues to dominate the way the "West" discusses everywhere else. You should definitely read it, everyone should.

As Said says:

"The idea of representation is a theatrical one: the Orient is the stage on which the whole East is confined. On this stage will appear figures whose role it is to represent the larger whole from which they emanate. The Orient then seems to be, not an unlimited extension
beyond the familiar European world, but rather a closed field, a theatrical stage affixed to Europe. An Orientalist is but the particular specialist in knowledge for which Europe at large is respon­ sible, in the way that an audience is historically and culturally responsible for (and responsive to) dramas technically put together by the dramatist." p.63

One of the pillars of thought of Orientalism is

"there is the motif of the Orient as insinuating danger. Rationality is undermined by Eastern excesses, those mysteriously attractive opposites to what seem to be normal values." p. 57

Therefore it is impossible that one of the supports of "Western thought," the university, could exist anywhere but the West. And thus the religious aspects of al-Qayrawan and al-Azhar are emphasized to make it clear they are religious schools not universities, ignoring the fact that religious study played a big role in Western universities as well.

Now interestingly there is actually a huge study by George Makdisi, full disclosure he was the adviser to one of my PhD advisers, called The Rise of Colleges which argued that the Western university system was heavily influenced by Islamic thought.

In his conclusion he provides an eighteen point list of major confluences between Islamic legal schools and what would become the "Western" university. For example, he finds a strong link between the summae Ibn Aqil and Thomas Aquinas. You should read it as well and decided for yourself. That brings us to the larger question of why it matters who was first? In Makdisi, it was written thirty years ago, there is a sense of it reclaiming an Arabic spot in the intellectual tradition and redeeming a tradition that is ignored. But it remains a question whether having "the first university" really does anything.

Also, does it matter that there were other non-Western places that had universities even farther back, like in the Indian subcontinent?

Sources

Edward Said, Orientalism Pantheon, 1979

George Makdisi, The Rise of Colleges: Institutions of Learning in Islam and West (Edinburgh: Edinburgh Press, 1981)