First and foremost, it's not just Hams that do that. GMRS based CERT and REACT team's (who are often not Hams) handle nets and emergencies the same way ARES/RACES does. The reason for this is because emergency communications has been standardized in the US and anyone who want to help is going to do it the formal way.
Secondly, I think you are misunderstanding the concept of calling for emergency or priority traffic. If it was EmComm traffic, operators move from local, up to regional/national nets, and then back down to a local net. In a traditional communications blackout, that is how emergency and priority messages get handled. So, that is how they practice.
The whole procedure is not for the guy stuck on the side of a mountain... though if no one has been returning your call for help and you know a net is on a specific frequency and day,, you can bet your bottom dollar you will be thrilled they're on the air and they will take your emergency call.
Also, it's a good habit to get into in case there is a real emergency. Especially before a net or a bunch of long-winded people getting ready to ha e a BS session. It's a good idea to remind everyone that regardless of what they are talking about, all conversation should stop if someone with an emergency gets in the air.
If you don't want to listen to or participate in a net, no big deal. Just turn the radio off.. Don't trash people for caring enough to make sure there is no real emergency and practicing for the day one happens.