55e is happening because WOTC was more or less milking the core 3 books for sale for 9 years and they having invested enough into other streams to keep sales up when the core hits saturation.Because people are dissatisfied with the status quo. As WotC's own data shows.
There are plenty of other reasons--but that alone is enough. The status quo is a problem. If it weren't, we wouldn't have 5.5e.
5.5e is just them trying to milk the new core.
But there's no way that'll last 10 like the 2014 ones because the 2023 ones are still stick to paradigms and models that are 10 years old.
Like I said right above, WOTC still doesn't know what a level 1 ranger, level 6 monk, level 11 barbarian, or level 19fighter looks like