[ordu]

I believe it is due to technical problems of switching everything to DoH. Moreover if we think about it, I'll see that it is not a Google or Mozilla problem, it is a problem of OS developers. For example, it might be done by gethostbyname using DoH to resolve names. But it is up to libc developers, and it would lead to other problems, like system after update stopped working, due to custom configuration incompatible with DoH.

Mozilla and Google become unsatisfied with gethostbyname but they cannot change that part of OS. So they are solving their problems on their side.