Someone just pointed this out to me from the Midwest Political Science Association conference webpage:
When the MPSA negotiates a contract with a conference hotel, the association receives free meeting space in exchange for a guarantee that it will use a specific number of sleeping rooms. If attendees do not use the required number of sleeping rooms, the MPSA must pay the cost for these unused rooms, which could amount to hundreds of thousands of dollars. In addition, the more sleeping rooms that conference attendees use, the more attractive the MPSA conference becomes to a hotel, and the MPSA can negotiate even lower room rates. In essence, the attendees who stay outside the conference hotels are "free riders."
WTH? It costs $90 for a graduate student and $180 to register for the conference if you do so early and stay in the hotel. They jack it up if you don't stay in the hotel. Meanwhile, the special conference rates for the hotels are all over $200 a night, even for a single. The only other option they'll accept is a hostel.
Whoever wrote that may have a very generous travel budget, but most people don't (and grad students often get nothing). Even a reasonably generous travel budget will be entirely blown very quickly. Considering people "free riders" when in fact they are just trying to make ends meet is excessive and insulting.