Unfortunately as they got popular automated translation services got good enough that nobody was going to pay for a slightly better and slower translation enmass.
Once that happened, that's when it seemed like they dumped their goals of teaching language and instead focused on dark pattern money extraction.
To be a bit cynical about it: the typical DuoLingo player has probably been misled to some extent about its effectiveness, yes, but also many of them don't particularly want to learn a new language. I suspect that they're happy to be able to play a popular mobile game that everyone else is also playing without the stigma of being a "Candy Crush addict" and "timewaster". "I'm learning a language!" is the welcome figleaf. https://youtu.be/F3SzNuEGmwQ?t=243
It drives me nuts that Duolingo's Japanese course does not explain grammar nor does it introduce new grammars fast enough. It's super boring to see です and ます most of the time, with occasional new grammar points thrown in. It's also strange that Duolingo introduces honorifics without context. This is super confusing. Who in the world would decipher a long string of characters out of a few really bland sentences?