I'll add:

- Telegram had usernames in 2014 before Signal added them a decade later, allowing people to chat without sharing their phone number

- Telegram has unencrypted chats which allow for giant chat rooms of 200,000+ and channels with millions of subscribers. Signal warns about performance issues when you have more than 150 people in a group. Telegram isn't just a messenger - it's often used as a social publishing platform like Instagram.

I don't use Telegram and use Signal a lot, but I also understand why other people use Telegram: the same reason they use Instagram.