I wouldn't say it doesn't offer E2EE by default. It offers private chats, which are E2EE, right there and almost as easy to initiate as the regular chats.

I used Telegram in E2EE mode with someone initially, but later we decided the multi-device sync and web chat were so much more useful to us, it trumped the desirability of E2EE and we switched.

Those features together would be better of course.