Because you're normal!
There's a mom at our gym I've known for a while as our girls were in rec together...my DD was asked to join preteam, and is now on team, while her girls are still in rec. I can see on her face that she questions why my DD has advanced and hers haven't (and honestly I'm puzzled as well), but she'd never say something to my face!
Luckily our viewing area is technically a "no drama zone" so it somewhat keeps these situations to a minimum, I do over hear the jealousy crap every once in a while though. I guess some mom's just have nothing better to do.
Makes me think of a sign I want to make and post in the gym...it would read:
Things you (parents) could be doing instead of sitting here spreading gossip:
Go home
Go to the store
Walk around outside
Work out (we have a fitness center attached)
Eat
Clean the bathroom
Feel free to add ideas