iOS 18 came out as a beta first for a bit.
In fact it's still in Beta with 18.1
Perhaps you prefer unstable software with glitches and apps that app developers haven't sorted for the new software
Personally, I prefer software to come out when it's ready
Apples software is much more limited to just a handful of devices, and all work on the same sort of platform. So it's much easier to develop
Android is software that has to work with a vast array of models and makes. It naturally will take much longer, and although One UI is a small part of this. It still has a large model range to be optimised for
Software also needs critical and main important apps to work with it. So, it can't be released until app developers have had time as well
To me One UI 6.1 works great so I'm in no rush to get any new updates. Security patch updates are more important to me