At any rate, the discussion going on here is about how Durov has been arrested because Telegram refuses to respond to law enforcement requests, when they do have the ability to do so; and if they were to actually implement E2EE by default (and for group chats), Durov would likely not be in trouble, since Telegram would be unable to provide anything when requested.
I suspect that isn’t the motivation. GDPR says that you have to give users choices about data stored like this (including right to be forgotten, how it’s processed and used and so on), and this becomes a technical, legal and commercial nightmare very quickly. The easier route is just to get rid of it if you can.
This saves Google money (it likely wasn’t that useful to sell to advertisers), makes legal compliance a lot easier and de-risks them from very large fines.
I suspect that the EU lawmakers didn’t think about second order effects like making it harder for law enforcement to access this data in scenarios like this.