I think there are a few things going on here -
With SAHMs, I've noticed a lot of effort in trying to get kids out of their hair. And then they complain about how "busy" they are.
Which brings me to my 2nd annoyance - I am so sick of hearing the "I'm just SO busy... I couldn't possibly fit in 3 hours for you 2 weeks from now. We have playdates, swimming & summer camps & a gazillion memberships to every place in the city." Really? Get over yourself. So, you don't even have time to eat, then?! No one's THAT busy. I think that some people tend to embellish how "busy" they are to feel that they are important.
I thought we'd be busier, too. Everyone says "let's hang", but then when it comes to actually figuring it out, they always have something to do. Whatever. God forbid your kid had some down time.