I bet on the latter. They could easily increase the number of people allowed to attend those event, making the parks more crowded. But this wouldn't create the same positive buzz of livebloggers commenting how lovely the event is (now even with a free dinner!). People will read and watch all those positive comments and just ignore the few comments of people that couldn't book them (they'll probably wrongly assume they just didn't plan well enough). They do not care about making all of us happy, they care about having a powerful marketing tool. Booking the parks for more nights and fixing the website cost money, why spend them when the events work so well already (from their point of view)?
I'll try to book the DHS event in a few days, keeping my fingers crossed already and getting prepared for disappointment.