You are confusing police chiefs with county sheriffs.

I am not. It's not universal, but many municipalities have an elected police chief.

Overall, it seems less common than you aver. What percentage of cities do you think have elected police chiefs?

Name any US jurisdiction with an elected chief of police.

San Angelo, Texas.

It used to be more common, but most places switched to appointment by the mayor or city council or city manager. Now it is mostly just a handful of scattered cities in a few states, with the exception of Louisiana where I believe they are still mostly elected.

The city I live in, Santa Clara, has an elected police chief. It's common, though not universal.