1. why do everyone insist E2E-encryption is necessary for IM but not for email and letters ( the alternatives)? Because that is mostly what I use Telegram for.

2. I could have a hard time choosing between Signal and Telegram some days. With WhatsApp I know Facebook will do metadata analysis on my contacts and my conversations (possible even with E2E-encryption). They'll also upload some or all my messages unencrypted to Google if I or any of my contacts enable backups.

Does that explain it?