The regular chats are encrypted though, just with an (encrypted) server in the middle. Telegram also claims in their FAQ, that no one singular person has the power to decrypt and the keys are stored such that no singular government could force them to give up any data.
How far that is true is a different question though.
You got it the wrong way round. It’s awful because it is the most popular os. If you look back at Windows XP or 7, they were clean, consistent and a pleasure to use. Everybody had XP, then 7 and by then it was too late and everybody was used to it and Microsoft can do whatever they want now and people will just take it because they’ve always used Windows. No need to put in effort.