While I can see your point, I think you simply demand too much. I’m quite certain that Fairphone has done some market research and executed a cost/benefit-analysis on this and concluded that it would most likely not be worth it at this point. As a small company they can’t focus on everything at once.
Personally I don’t really understand the love for Sailfish. Large parts of their operating system are still closed source. Some parts are open. The same holds true for Apple. I would not trust them more or less than Apple as both are companies who want to make money. Apple is doing a good job of being fairly secure, so your use-case is pretty much already covered.
As for privacy and alternative OS, Fairphone has already anounced their coorperation with /e/
https://twitter.com/Fairphone/status/1443592315168251904
and therefore they are doing their best to provide a Google free Android experience on the FP4.