Because its not normal here. Its sounds strange and.. well not forced, but not natural. Here no one is taught to say it as a polite thing, though obviously some people pick it up. So it grates when I hear it. Ma'am is associated with OLDer women. What woman wants to be told she is old?
Here it is used for respect and politeness. It doesn't mean you're old or older. Someone calling you ma'am, isn't calling you old.
I just can't understand being offended by someone saying yes, ma'am/sir. Now if they have a sarcastic attitude, THAT would be what the problem was, their attitude, not the words they use.
I think that people these days are really lacking in respect, and so I feel like we should encourage parents to teach their kids to be respectful, instead of getting upset because the parents are teaching their kids to show respect by calling someone ma'am/sir or Miss/Mr. I feel like it is more disrespectful to try to undermine the parents, when they are trying to teach their kids to show you respect.
But again I'm from Texas, and I guess we do a lot of things differently here.