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Video games are a visual medium, if you're not /showing/ the Pokemon getting stronger in a meaningful way what's the point? The whole reason people don't like Dynamaxing is that making every Pokemon just get bigger + have clouds overhead is less interesting than giving a limited pool of mons new forms.
You have to remember that the main appeal of this franchise isn't competitive battling, it's the monster designs. Megas were a good gimmick because they did something interesting with the monsters, making them a silent stat buff is boring.