Because religion matters. In this case, islam has a millenarian, worldwide record of massacring non-muslims so it doesn’t seem far fetched to impose boundaries based on this criterion. Also the Pakistan+Bangladesh/India partition was made on this religious clivage, so muslims have two others countries to choose from.
As someone who almost lost a friend in a jihadist terror attack, I’m really upset when Westerners purposely turn blind on the muslim civilization misdeeds. If almost every other civilization hate them it’s for reasons rooted historically (aggressive expansionism in Middle-East, India and Europe) and killing of innocents people that happen every day around the world because they don’t believe in the muslim god.