I'll try to type slowly for you. In Revelation, the chapter and verse you quoted earlier, it says there are thousands of beheaded believers seated on thrones, or something like that, will sit in judgement.
I'm just guessing that those who believe the bible is the word of god, and take at least the NT literally, would conclude that certain things have to transpire before there can be whatever you call the 'end times'. One of those is thousands of beheaded Christians. ISIL is facilitating this for them. They can be done with this temporal world sooner.
Sort of like me coming out and taking 20 crappy stops from you so you can go home early on Friday.