Chats are encrypted. The question who can decrypt them by default.
It is a trade-off between security and usability. By default, you get usability (e.g., you can chat across devices easily). But you think it is worth the cost, you can make encryption keys unavailable without corresponding devices (create secret chat).
My guess, most telegram users prefer usability or don't care/ignorant. It would be a mistake to make the experience worse (that people would notice ignorant or not).
It is a trade-off between security and usability. By default, you get usability (e.g., you can chat across devices easily). But you think it is worth the cost, you can make encryption keys unavailable without corresponding devices (create secret chat).
My guess, most telegram users prefer usability or don't care/ignorant. It would be a mistake to make the experience worse (that people would notice ignorant or not).