I like organized rides for a lot of reasons.
First, it's great to support a good cause, and I feel like I'm doing something more than just writing a check. OK, sure... if I just wrote the check and didn't ride, the charity would net more $$, but it's so impersonal.
Second, it's a great way to get a long ride in where you don't really have to THINK. There are always plenty of stops that will always have food, water, and sports drinks. No need to bring cash or a Credit Card to pick up more snacks on the way - or worry about being out too far and running out of water/food with no open gas station in sight. No worries about mechanical problems. Sure, you should have your own spare and pump, but you don't have to stress about what being stranded if you suffer a major mechanical.
Third... Plenty of riding options. I like riding alone. I like riding in groups. But doing either all day is boring. On a charity ride, I can ride for an hour with a pack that's going faster than I can handle all day, then drop off sometime after I do my pull, ride solo for a bit, join a different group, and repeat that all day until I'm either in a group that matches my comfortable pace, or riding solo across the finish. And I get to meet a ton of people that way - many of them several times, as I tend to be in and out of rest stops a lot faster than most riders.
Fourth... No club-related drama.
Fifth, I've never been ridiculed for the type of bike I brought to a charity ride.