That's because Muslims were only given 1/3 of the ghay (gee) or region of the Roman earth to conquer, which was the western half. They are the locusts of revelation. The other 2/3rds were given to others.

Bellarmine also collided with Ribera to create the futurist approach to the books of Daniel and revelation which were against how the church understood revelation up to that point. They made it up to deflect from the Protestants pointing the finger (correctly) to the Pope as being the man of perdition. Unfortunately Protestants finally succumbed to this teaching when Scofield came onto the scene along with Darby and popularized it in our circles.