Same reason a bunch of mons got banned because of Z-Move-related reasons but not Z-Moves themselves.
Which ones?
2 at most?
Most of gen 7 bans consist of megas which can't hold z-crystals, blaziken who was banned 3 gens in a row regardless, lando-i same reason banned for 4 gens in a row just too 'OP', 2 ultra beast with only 1 of them being a z-crystal user, and aegislash who was banned for centralizing the tier.
Out of all the ubers, only naganadel specifically was banned for z-crystals and that's debatable seeing how it was still broken in gen 8. Aegislash is the only one you can argue might've been pushed by ghostium-Z but it was mostly how it still centralized the tier just like gen 6.
The claim Z-moves got anything banned needs some serious citation around here.
We're already looking at a lot of mons that would've been quick banned or suspected by now if it wasn't for the debate of whether or not tera stays and finch trying to give us opportunity to voice opinions and vote rather than council ban half of OU straight away. This is very comparable to dynamax where it would've contributed to targetting half the tier because of it.
So you're telling me that there is a plan to deal with Espathra at +2 SpA/SpD/Spe? That mon has STAB Stored Power and Dazzling Gleam to smoke Dark-types trying to counter it. All it needs to do when something that tries to kill it with Sucker Punch switches in is click Sub.
That shit is broken WITHOUT Tera.
Espathra is pushed very over the edge by it. Swapping from psychic type means you can't blanket check or counter it with 1 mon (chi-yu and kinggambit would be solid counters without tera-fighting.)
+1 0 SpA Espathra Dazzling Gleam vs. 252 HP / 0 SpD Kingambit: 100-118 (24.7 - 29.2%) -- 99.9% chance to 4HKO
+2 0 SpA Espathra Dazzling Gleam vs. 252 HP / 0 SpD Kingambit: 133-157 (32.9 - 38.8%) -- 99.8% chance to 3HKO
+1 0 SpA Espathra Dazzling Gleam vs. 0 HP / 0 SpD Chi-Yu: 74-88 (29.4 - 35%) -- 15.2% chance to 3HKO
+2 0 SpA Espathra Dazzling Gleam vs. 0 HP / 0 SpD Chi-Yu: 99-117 (39.4 - 46.6%) -- guaranteed 3HKO
Add tera fighting into the mix:
0 SpA Espathra Tera Blast vs. 252 HP / 0 SpD Kingambit: 400-472 (99 - 116.8%) -- 87.5% chance to OHKO
with 0 setup, can KO kingambit. Guaranteed with rocks.
And if we take the above calcs and apply
fairy STAB to them:
+1 0 SpA Espathra Dazzling Gleam vs. 0 HP / 0 SpD Chi-Yu: 111-132 (44.2 - 52.5%) -- 18.4% chance to 2HKO
+2 0 SpA Espathra Dazzling Gleam vs. 0 HP / 0 SpD Chi-Yu: 148-175 (58.9 - 69.7%) -- guaranteed 2HKO
+1 0 SpA Espathra Dazzling Gleam vs. 252 HP / 0 SpD Kingambit: 150-177 (37.1 - 43.8%) -- guaranteed 3HKO
+2 0 SpA Espathra Dazzling Gleam vs. 252 HP / 0 SpD Kingambit: 199-235 (49.2 - 58.1%) -- 98% chance to 2HKO
Now it goes from needing 3 calm minds to cleanly get a 2HKO, to only 2. idk what you're doing if it gets 3 turns of calm mind, it only gets 1 free from switching into it, 1 from breaking the sub, and it shouldn't be greeding for the 3rd cause it gets 2HKO'd at that point, not to mention removal of psychic removes that ability to 2HKO it.
Chi-yu/kingambit's presence in the tier alone holds it back from what its currently doing, much like how heatran held back volcarona. You just slap it on the team, and now espathra is a BL tier mon against your team, currently you need multiple checks because it runs through your team if you guess the wrong typing (usually its fairy but ig fighting could work too), or if you overprepare for its alt typing it might not tera at all and run down teams.