For those that grew up going to Ocean City (I am sure its the same for the Jersey Shore), there is just that nostalgia factor coupled with convenience. Its within a 4-5 hour driving to millions. The last census said about 7,000 live their during the winter but on a summer weekend there could be 350,000 people visiting.
Some people think, oh its so hard to go to that it must be really nice. Not really. It is what it is. During summer a flea bag motel across coastal highway with a parking lot view can go for the same as a moderate Maui resort 1BR with ocean side view. A Milkshake at Dumsers Dairy land is now over $7.00 for at 16oz. The Ocean is quite cold even in June and July to those who are used to it SC and South.
I worked 2 summers in Ocean City (one in High School and one in College) but had avoided it in summer for a while preferring the nice timeshares in Virginia Beach and Myrtle Beach (but also a longer car ride). A couple of years we started going again and it is a fun place but a more local perspective helps and I would never recommend Ocean City, Maryland to anyone who has to fly and then drive the 3+ hours or even drive more than 5 hours total. There are probably just as nice or nicer places for those visitors.