Why is "sub par" bad?

'Sub par' means 'below average' or 'below reasonable expectations'. 'Sub' always means 'below' or 'less than'.

In a game where beating the average number of strokes is a sign of quality of play, 'sub par' is good. If your heart surgery was 'sub par', that would not be good. If the quality of the building work on your house was 'sub par' that would not be good.

Sub means "under" as it does in golf.  So, if you shoot under par, you shot a sub-par round.

Not a golf metaphor because it wouldn't make any sense. "Par" is +1, so SUB-par can just be 0, which is AVERAGE

I dont think that the saying originated from golf.

Because it means below averagre or below expectations.

Because its not just a golfing term, although its most commonly used in golf. It means an expected level or standard, so the par rating for a golf hole is the standard number of ahots it should take to get in the hole. So sub par means below standard

I never believed it to mean bad. The way I have used it for example, If someone is cocky and claims to have done a perfect job. I may exclaim, “It was sub par.”

Excellent point, yet it translates to something falling less than an expectation or established criteria