1) Because it is not a widely accepted POV, although there is overwhelming evidence for it.
2) Because Classic Islamic philosophy is often seen as mistaken by Scholastic philosophers (even if Scholastic philosophy would not exist without Averroism) and those philosophers are the precursors of modern philosophers.
3) Because Ancient Greeks are considered Western but Islamic caliphates are not.
4) Because the Crusades were associated with significant revisionism, including book burning of Arabic books, which makes it harder but not impossible to susbstantiate this POV.
5) Because some people (usually the far right people that listen to historically inaccurate podcasts and radio shows) believe that the West civilized the world and a POV that sounds opposite to that and credits their religious/ideological adversaries cause them to become very, very upset.
Can down voters please explain why you disagree? (Unless hn is just overrun with deluded brainwashed lunatics.)