> But the open source project wouldn’t need to invest as much as Google does.
Not at first. Yet over time the work increases as one must differ more and more from Chrome. I believe that's why so many forks are giving up on Manifest V2.
Differentiating isn’t as important as not engaging in Google‘s heinous practices
Forks are giving up on mv2 because it's not as important as the people online say it is. If mv2 was what would cause a browser to gain market share they would keep maintaining it, but if the market is not rewarding browsers with mv2 then it does not make sense to maintain.