For one thing, Hershey is a brand that people know and recognize, and therefore you don't have to do a lot of explaining about the product or what it is.
Secondly, people love chocolate, and we have all their favorites in our Hershey variety boxes. Hershey fundraisers are about as close as you can get to having a product that sells itself. All you have to do is show people what you have, and let them choose what they want.
If you are organizing a fundraising effort for a school or other youth group, chocolate is a natural choice, and Hershey candy fundraisers are just about the best idea out there. You probably already know how picky kids can be about their favorite brands of things - they want what they want, and they'll accept no substitutes.
Hershey fundraisers really appeal to kids for this very reason. This is not some no-name chocolate they've never heard of; it's a box full of all the candy bars they would normally buy anyway. If you can get permission for the kids to sell on school grounds, that's really something to get excited about with Hershey fundraisers.
Lunch periods and after school are prime times for people wanting chocolate, and being in the right place at the right time is often all it takes. You can see how a fundraiser like this could easily snowball - you may find yourself ordering more product after the first week.
There's really no limit to the amount of money you can make with Hershey fundraisers, and if you're working with kids, it's pretty much a no-brainer.