Easy for the Brave CEO to say they keep ManifestV2 support while these enterprise flags in the Chromium codebase are still present. Once these flags are removed, and the code is removed, and then the internal APIs to support the ManifestV2 code is removed it becomes a whole other thing.
You can try to keep the code, but every upstream code change becomes more painful to integrate. It is going to cost more and more, requiring more and more expertise with the Chromium codebase, like it is some kind of technical debt. Not even counting the potential security issues you can introduce by keeping the code alive, with Brave being a target that is large enough to matter for hackers but perhaps too small for security researchers.
The Brave ads cryptocurrency stuff was/is a turn-off for many. That'd be my guess regarding the downvotes, anyways. As well as the Brave redirection to affiliate links left a sour taste.
For me, at least, it's not so much the crypto ads in of themselves that puts me off Brave. The issue is that they are a manifestation of Brave's fundamental problem: It's a for-profit endeavor based around offering a free product.
The money has to come from somewhere.
All other browsers have some kind of reasonable story behind the investment made into their existence (yes, even Chrome). Brave doesn't have any, and if the crypto ads stopped paying the bills, there must be something else that comes around to do so. Frankly, I wouldn't trust anyone who's put in that sort of situation with a piece of software I use to access anything important. Doubly so if crypto is a load-bearing component of the current status quo.