Keep in mind the times: When ZZ started using drum machines (and Frank used triggers live onstage) guitar rock from the '70s was a dying (or dead) beast. When ZZ ruled MTV, where was Mark Farner, Frank Marino, Trower, Nugent? ZZTop survived by adApting, and adOpting the sounds of synths and drum machines. A whole new audience.
Remember when Bruce Springsteen started using synths "Dancing in the Dark"? Petty did ("Don't Come Around Here No More"), Van Halen ("Jump"), etc etc. To many rockers, that was practically "disco", or a move to it! But, it worked, and kept them current and on the charts.
In the case of drummers, natural human feel was OUT, and everyone was a slave to the machine rhythms. I mixed a Doobies track - the last studio recording with Michael MacDonald. The drummer was ON there, but he only played VERY VERY stiff - just like a drum machine - all the way through the song! Oddly enough, to further push the "drum machine" aspect, he had but ONE track, all the drums submixed in mono!
David Robinson of the Cars is one of my favorite drummers of that era. Listen to their first record and EVERY drum fill is memorable and musical as hell. By the third album, HE was a drum machine... they credit him, but it isn't him.
Just because I am odd, I still use an 80's programmable drum machine on pop and rock records... the samples aren't great, and we don't use loops. It does work - it's just a weird time that people don't accept that now...