OpenTable came into existence because of simple value proposition. For the restaurant, it simplifies the process of booking reservations. For the diner, it provides an easy way to access availability of any given time slot quickly across many places. Seems like a solid business that provides a nice service.
Unfortunately, that's not enough.
They took a big fat IPO, sold a couple times, and are now owned by Priceline. If they don't do the "surveillance capitalism" thing, that makes them a money loser-- given the obscene amount of money pumped in to "scale" them.
The best thing we can do is to make a phone call to the restaurant instead, or, just show up and hope for the best. Perhaps in time the restaurant industry will come up with an open standard webservice to do this stuff instead of depending on OpenTable, but I won't hold my breath.