Google Chrome, Microsoft Edge, and Brave all are made from what is called Chromium. This means there are many similarities, but then each company modifies the code for their own purposes. A lot of the extensions people use were made specifically for Chrome. Though this is a poor analogy, I guess it’s a way to depict it.
When an extension is made for Chrome, it is given a specific set of keys so it can do its job. It understand what should be displayed and what types of modifications can be done. When you then install that extension on Brave, it tries to use those same keys and paths that it is familiar with. The problem is Brave has extra doors and the passages are different, as they are more privacy focused. So when you add your extension to Brave, it might do okay but it might also fight with Brave as it wants access to places that Brave has secured. The browser might open the doors or have limited access, but it’s like a security officer at the door. As you can imagine, this would slow things down or prevent the extension from doing its job.
Again, what I gave is a VERY BAD analogy, but is at least a sincere attempt to show something as I’m very tired. I mean, other ways to think is what happens if you put something that was designed for iPhone on Android? It doesn’t work, right? That’s because the languages from each are different and not compatible, so they have to be modified to work on each. It’s similar to extensions. While they try to keep things standardized enough for many extensions, there’s a lot of ways it can go wrong depending on which one you install and from where.
Edit
Apologize, as I saw I don't get your point
when you said you do get my point. So I kind of rambled on things I maybe didn’t have to, but maybe it helps others if nothing special for you.
And yeah, Brave is always evolving and working to make things better. Just keep in mind when having things like Extensions, it also is going to take the people designing the extension to make sure it will be compatible with Brave as well.