Because unlike with Facebook no one has been able to show a single example of Telegram abusing their customers even once.

Let me use an example:

Would you want to ride the absolutely bulletproof and soundproof taxi that has one disadvantage: that it is well known that the drivers make notes about who you are and who you visit and sell that data to companies like Cambridge Analytica?

Or would you take another more ordinary taxi that might not be armoured and soundproof and might or might not log your visits - but at least no one has caught them red handed?

The answer depends on who you are I guess: [edit: if your main fear is that someone might be listening to your conversations and you don't care if the known shady taxi company logs who you visit, go with armoured, bulletproof taxi. I admit] there are times when E2E is a massive difference but for me this is mostly about preventing future Cambridge Analytica situations.

That depends whether shooting at taxis on the street is a regular thing.

I think that was GPs exact point:

there are times when bulletproof is important and in such cases you absolutely should go for it.

But most of the time and most places it is just a giant waste.

Because Telegram doesn't gobble up all your metadata to sell to advertisers & malcontents. Who you talk to at what moment and from what location is equally as valuable as the content of your messages.