It's because Google's UX designers don't care about their users. They only care about getting promoted. Redesigning everything to be flat is a lot of work so

It's because Google's UX designers don't care about their users. They only care about getting promoted. Redesigning everything to be flat is a lot of work so a lot of people can get promoted doing it. We can all blame Matias Duarte for creating and launching Material Design without performing any usability testing. A few days before the public launch, he presented Material Design at the Google all-hands meeting and admitted in the Q&A that they had just started usability testing. I predict that everything will be flattened by 2024 and they will begin adding back the affordances. Then it will take a few years for other companies to start adding affordances back. Everything will be usable again in 2029.