If Palestinians were not mostly Muslims, hardly any Muslim would give a damn about Palestine.
They only care because they consider Palestine part of the "ummah". If they were mostly Buddhists or Christians, Muslims wouldn't bother with it just like no Muslims ever protest about Ukraine, Tibet or any other case.
Muslims don't truly care about Muslim lives anyway - demonstrated by their silence on the conflicts in Yemen, Syria, Sudan, Somalia, Nigeria, etc. In most of those situations, Muslims are killing other Muslims or they're killing Christians (like in Nigeria), so it doesn't register for the Muslim diaspora to care. No hysterical protesting. No calls for boycotts.
Israel vs Palestine animates them because it hurts the collective Muslim ego to see a formerly Muslim majority land get usurped by a group of non-Muslims. They want to recapture the lost territory for the Islamic ummah and deliver pride back to Muslims.
Muslims - stone age primitives that they are - only derive pride from the physical conquest of territory and dominion over it; not from much else. As Israel delivers more and more humiliation blows to the Muslims in Palestine, Iran and Lebanon, the collective pride of Muslims continues to shatter and their rage will only grow more uncontrollably violent.
You don't even have to like Israel to recognize this truth about the Muslim ego.