why there is a limit on how many extensions we can have
The true answer is that the list in prefs can’t scroll and if it goes linger than a certain amount then the bottom item in the list will fall off the bottom of the screen. And so the current limit is based on the smallest typical screen size.
You may think that is ridiculous, I could not possibly comment 
However, you can increase the limit, see: Lots of extensions - expand the list - #4 by nick
Thanks for posting and welcome to the forum.