What's with the endless re-formations/'don't look back' gigs..?

This has confused me, why do people go and see has beens churning out the hits/classic albums when they're all so obviously out of shape/past it/should know better....?

I've always had 3 rules

1. Never go and see a band that formed a great part of your formative years listening experience when they're past it creatively.

2. Never go and see a band that formed a great part of your formative years listening experience that you didn't see back in the day (eg at their peak when you should've seen them) and they're now past it.

3. Never go and see a covers band of a band that formed a great part of your formative years listening experience.

Why do people do it, surely its just shitting in the face of your memories...?

Or am I completely off here...?