Alas, that is one of the great mysteries. The all-knowing Creator knew when he created Lucifer what was to come. Hopefully, we'll know the answers when we get to heaven.
I think it has something to do with the laws of the universe -
- you can't have day without night,
- cold without hot,
- love without hate,
- good without evil.
If He has kept things in balance, there must a lot (one billion plus) saints with us today to balance out all those Muslims.