Thunderclap is also limited to 4 targets in classic.
Back when I was arguing extensively with ghostcrawler/blue devs when they were developing wotlk and talking about balancing tanks for single targets, I coined the term “multimob” tanking… essentially paladins are/were the only tanks capable of AE tanking (consecrate + high reflected damage, doesn’t matter how many extra mobs are in an area, the threat per mob remains the same).
Both druids and Warriors could only “multimob” tank, as every one of their abilities had a target cap (druids had thorns but it was insubstantial)
swipe was 3 targets everything else was 1… Warriors have 2 target cleave (on next swing) and TC in battle stance of 4 targets. Thus once you go above the target caps of abilities even if you perfectly distribute threat you start generating less and less threat the more mobs there are.
The Dev’s solution to this was to make thunder clap useable in def stance, remove its target limit and do an insane amount of threat to match the output of paladins, druids got no target limit swipes and DKs got DND, pestilence, blood boil heart strike cleave etc… and thus we got the WOTLK trolololol dungeon modes and modern wow tanking style.