On one end by almost literally being an extension of Google. On the other end by constantly laying off engineers. A big problem people are just handwaving away is that browsers are incredibly complex nowadays and how do you fund development of a browser engine? If you think the "Linux" model would work, well browsers already have that - it's called Mozilla and there is never any good news about them.
Brave is also funded by Google - Brave doesn't develop a browser, they develop a skin around a browser engine that Google pays millions to develop and has decided to open source.
There is also another aspect to it - one can imagine that the time of an OS which would run web apps as first class citizens (in the correctly engineered sandboxes/etc.) just hasn't come yet. In the meantime the browsers are just ugly stop-gap 0.x version of such an OS (there is a reason they are "browsers" as their roots (incl. deep architectural roots) are in browsing of static content, and everything else is bolt-ons - the integration of JavaScript engine for example back then could be best described exactly as a "bolt-on").
Not really the best examples.