People stop using things which don't work or stop working on the regular.
Its not a marketing problem, its a market problem.
The only money in the current market is in ads/surveillance and that's basically a requirement to compete. They can't achieve the same level as MS or Google because of sabotage, and an adverse market.
In some circles its called tortuous interference of a contract, but the bar to prove it is impossibly high so companies can strategically make changes to dependencies that force costs on a competitor as a dominant market player.
Do you know how many times Firefox has had bug tickets opened for Google, and Cloudflare, and others where those companies basically broke the web for everyone on that browser because their silent internal changes to captcha's and other systems didn't play nice with competitors browsers which respect privacy more than others? Change management is a solved problem, so the only reason this happens is because of purposeful asymmetry here where FTC enforcement has failed.
These breakages happens a lot, every few months on the regular going back more than a decade.
How do you attract people's attention to use your browser and deal with the brokenness, when competitors constantly break it? These type of toy projects.