

It might be the part of it, but other (maybe main) reason is probably the fact that they had significant crunch culture going and high turnover. They supposedly had trouble recruiting at some point due to running out of interested game dev programmers in Poland. And why take months to train recruits to use your in-house engine, that also requires a lot of work and resources to maintain, when you can use one everyone knows and do simple onboarding.
If you don’t have google play store or even have it just deactivated you don’t get ads or have limits for some activities in duolingo, as those use gems or whatever else is their virtual currency called, so you get way better experience overall.
At least it still worked like that about a year ago.