I'm trying to empathise with them... I get why people become radicals of other kinds... but saying no music, no sex, live by the book, behead those who disagree... what part of that makes people think "I want to get into this, this sounds fun"?
The Arab world has valid grievances, which motivated 9-11 for example, but there's more to it than that.
this is like asking why people get into religion generally, the flavor of religion seems to be fairly irrelevant for it becoming a murder-justification. i won't speculate or pontificate on 'why religion' because i'm irreligious
materially, Wahhabists are successful in radicalizing people because their preachers & groups are backed by Saudi Arabia & the CIA, but it's not like they invented the concept of murder + martyrdom