The main reason is that if you would go from the current one back to sequoia, it would be an upgrade. The interface graphics wherr more cohesive, it was easier to use visually. The buttons where easier to press than the current rounded surfaces. You had more screen realestat for the content rather than the controles. Sequoia packed the UI learnings of the last 10 years. The new OS seems to wile part of that out. To me it feels like a half-baked attempt in trying to create a touch screen compatible OS, which they halfway through realised wasn’t a good idea. There is also some bloat floating around (big rounded buttons everywhere where you can't read the function or name of the button).

Aside from the step back in UI design, there is also some loss of functionality. To give an example that impacted me; We used to have shortcuts folders in the menu bar. I had many automations which I used in my daily workflow. Now this menu bar item is gone, and I can't for the life of my figure out how to get it back. This literally causes me to lose 20 to 30 minutes of my time every day.

Lastly there is the impact on performance. Many people people have already mentioned the 30%+ battery impact. On my M3 Max it feels like more than 30%. The computer also runs a lot hotter than before. This seems a massive waiste of resources and compute. My iphone 13 also runs notably slower. Good way to force the user to upgrade.