Why were the Jews killed in the 1500 of Spain?

Because of the anti jew riots. As a result many of the remaining jews converted to christianity.

Tens of thousands of refugees died while trying to reach safety. In some instances, Spanish ship captains charged Jewish passengers exorbitant sums, then dumped them overboard in the middle of the ocean. In the last days before the expulsion, rumors spread throughout Spain that the fleeing refugees had swallowed gold and diamonds, and many Jews were knifed to death by brigands hoping to find treasures in their stomachs.