Other than legacy stuff, I think the main reason programmers still use it is the fact that '1' is easier for them to call to mind than '256', or whatever else.

Other than legacy stuff, I think the main reason programmers still use it is the fact that '1' is easier for them to call to mind than '256', or whatever else. So when you're throwing a script together really quickly, you'll prefer to type SHA1 instead of anything else. At least that's how my brain works.