You clearly have no clue what OpenTable is and what it solves.
It's a seating and reservation management platform - an essential need for the vast majority of non-casual restaurants. It's implemented as a hardware/software solution that they install on premise, so it works without a network connection.
In urban markets, they are pretty much a de facto standard, despite being expensive and archaic. Their website and mobile apps drive so many reservations that restaurant managers are more than willing to pay the hefty fees. Those consist of an installation fee (hundreds $), monthly maintenance fee (hundreds $), and per-reservation fee ($1 - $10 per PERSON).
As a technologist working in the restaurant industry, I really dislike them because both their consumer and front of house software sucks so much. That said, they're a real business, with real revenue, solving real problems, for real customers. So yeah, go make a "website for hipsters" and wait for your $2.6bn payout, since it's so easy.