because they don’t serve you targeted ads. duckduckgo’s(and startpage’s) business model is keyword-based ads, for which they are getting plenty of revenue.
brave has other paid offerings like search without ads(premium), brave VPN, their own shitcoin(BAT) and so on.

as for the search results, I’m a software developer. most of the time I know what I am searching for, and I don’t want my search engine to go on overdrive and interpret it as something else. for me, duckduckgo is perfect. google, on the other hand, is worse for me for this and other reasons.
and there shouldn’t be much difference between duckduckgo and bing(sans account) since duckduckgo sources the results from bing.

I don’t know when did you last try duckduckgo, but I’ve been using it since 2015 and I’ve rarely been disappointed. in case i am missing on something, it’s just a !sp away(duckduckgo bangs).