I bet that 1234 is used more often because of the 4-character minimum, like PIN codes on debit cards. It's 4 characters so it's safe. 123, on the other hand, is not safe, because it is 3 characters. /s

My solar inverter admin interface has a certain 4-digit password. So I wanted to change it to secure it, and found out that it only allows 4-digit passwords. Luckily the access point can be set up with a higher entropy password though (it is constantly advertised and had a very "secure" 8-digit password by default, I think you can guess which one)