It's because a lot of "family" dining establishments went out of business and every type of "fast" establishment grew.

Over in say, Europe, the cost of commercial real estate is much lower (including more restaurants owning their own building) and governments simply covered lost revenue versus loans which enabled more full service restaurants to stay in business.

The fact is, full service restaurants are a horrible business model and most aren't priced appropriately (they should be priced much higher).