Every language is fundamentally broken from day 1, whether it is a known tradeoff or something that remains hidden for several years. Also, even if you had the perfect language with a presumably not-mainstream feature, you would have to make that feature somewhat known in the developer ecosystem (just look at Rust’s borrow checker, it does cause issues for newcomers as opposed to features already having an analog in other languages). While FP ideas were known before Java (ML predates it by quite a few years), it has become only recently more acceptable, so it makes sense to only know incorporate it into the language (and yet again, do note that FP is not a silver bullet so java has to let developers write imperative constructs just as well as before)