ZZ is actually rather unpopular and seems to have decisively lost its spot as a top tier method a few years back. The tradeoffs vs CFOP are generally not considered worthwhile, because an entirely rotationless solve doesn't make up for a dramatically more complex EOLine and harder xcross. Only ZBLL exists as the extant remnants of ZZ.
Q: Wasn’t ZZ an attempt to avoid the crazy ZBF2L algorithms and came after ZB? People understood the value of ZBLL (hell, even I wrote out all the speed-oriented algorithms for it) but everyone doubted the viability of ZBF2L, so they tried to find other ways of orienting edges. Or was ZZ around before and people just realized they could apply ZBLL to it?
ZZ is definitely younger than ZB, and I think that story checks out. ZBF2L just tries to orient LL edges with the last pair, while ZZ moves it to part of the EOLine/EOCross. In both methods, ZBLL can be used to do LL.