[Satan]

They do this because they know nobody will take heavy handed action against these groups.
What do they have to fear when they won't be wiped out in one stroke?
Terrorists of common this year view this as pure holy war, they aren't afraid to die one by one in suicide attacks.

They would be afraid to die all together without being able to inflict more casualties to those who don't believe in their beliefs.

Also, your source link is broken.