I guess it's just the idea the word "failure" connotes. Nobody wants to be seen as a failure in general, but to fail at something or to fail at an attempt at something, does not make a person a total "failure" as a whole.
It's like we need a different word for when we try something that doesn't work and then have to figure out a different way to do it. It is a lesson after all and how else are we going to learn? Just because we try something that does not get the end result we were seeking, it just means we need to try a different way, not that we are failures.
I really just think it is the word.
I agree that the word has a negative connotation for sure. It probably starts when one is a child getting told not to do this or that by parents. You know, don't colour outside the lines and so on. It becomes so ingrained in a kid and then they go to school and here the same thing. Wear your uniform, stand in line, talk when you're spoken to, write like this. One gets to work and...Same thing*.
So yes, it's the word, but there's other factors as well I think.
Also, people have the choice as adults to see the word for what it is and make a change. Most don't.