Any currency can be used for illegal activities. Why the dollar is the most popular currency for these purposes?
because dollar is the most common currency in the world.
In general, bitcoin has more prospects for use in this area, because of anonymity
Well, this is true, i agre with you.
Bitcoin sometimes perceived as the (wild west of finance), the cryptocurrency space has been connected to various scams, hacks, terrorist and other criminal activities which have taken advantage of this anonymity.