They are bigger. Not as easy to guess. More like pretty impossible. It's like not letting the user choose the password. That way they can't have a bad password.

It is relatively easy to pick a password length/composition that's pretty much impossible to guess, too. So the benefit you're list is for the company (that has to deal with people picking bad passwords), not the person using their site.

Heck, the company could easily say that your password needs to be 128 characters long and use multiple types of characters - and tell you to use a password manager (that both generates and fills in that information for yet).

But these same services are the reason why my passwords are as short as they are. They made me use 'short passwords' by putting upper limits on them.