I didn't join the PTA at any my DCs schools, because I already volunteer as a cub leader, which takes up a huge amount of my spare time. I have 3DCs, a full time job, and and elderly parents who live 100 miles away, so I have very little spare time as it is.
However, I would always help at school fairs etc, for just one hour manning a stall, or helping set up or clear away. I was there anyway, so it didn't seem like a big deal to help on these occasions, my other half, inlaws or a friend would take my kids around the fete while I did my shift.
200 people attended the event I planned today and had a good time but only 8 people volunteered to help
I totally understand that not everyone can help with the planning, not everyone has the time or inclination to do so. But surely more than 8 could have helped to man a stall. The 200 who were there couldn't possibly say they didn't have time, as they were there anyway. The OP had made it easy to sign up, for only 45 minutes help at a time. But still no takers.
I've noticed this with Cubs, to be honest. Parents are very keen for their kids to attend, and go on all the trips, camps etc, but are not so keen to volunteer to help out. Of course, everyone is falling over themselves to volunteer to help with the free, big day out we do once a year! But not so much with the day to day help needed at meetings, setting up tents, cooking at camp etc. I do understand why this is, but that doesn't mean it's not a bit disheartening.