It takes a huge, lengthy effort to make a browser that is close enough to standards compliance and performant enough that people would be happy using it. Even

It takes a huge, lengthy effort to make a browser that is close enough to standards compliance and performant enough that people would be happy using it. Even if you do all those things, there's little guarantee that your efforts would be noticed by many people, since you would need to do a LOT of marketing (especially to get your browser installed by default in MS/macOS worlds). The costs are just not worth the risk-adjusted rewards.