Considering the current bug where the kings can't be killed, and a draw in stage 3 is a win for the defenders, it's no surprise that people are stacking on the defender's side. As destro seem to have more success taking forts at the moment (for whatever reason), that will put them at a big disadvantage when it comes to cities:
https://github.com/WarEmu/WarBugs/issues/20044
Personally, having done cities to death in the first half of 2020 when they were new, were the "end game" and couldn't leave home due to lockdown, I am very tired of them. A lot of people (not all, but a lot) in my guild no longer have any interest in doing cities either, regardless of how the rewards go up and down either. For a fairly recent EU city - which happened to fall on a guild warband night - we decided to do RVR in Praag instead.
Even if the bugs were fixed, cities are no longer end game and not particularly fresh anymore. Personally no amount of war crests (well okay, I'm sure there's some threshold that would tempt me...) will entice me to sit through either stomping the enemy (honestly not fun anymore after 2 years...) or getting stomped.
Finally, the strats for cities are pretty much optimised these days and it often feels flow-charty. You know the most important fight on stage 1 is the middle BO. The warlord routes on stage 2 are known and cannot be influenced, and the warlords don't do anything interesting anyway. Other NPCs just serve as an annoying speed bump to be dismounted. Cannons guarding the BOs don't do anything useful, and unless something changed the defenders are actively discouraged from using them as it allows the attackers to come in with morales built up.
I'm hoping when the sieges are added to KaK and K8P that they come with brand new mechanics and are not a mirror of Altdorf/IC.