It is the busiest day of the year for most restaurants.
Most good ones are booked well in advance.
It is also the one day the EVERYONE who works for the restaurant has to work. Nobody gets Mothers Day off.
My wife worked for years as a waitress/hostess at several area restaurants. My son worked as a buss boy during college.
I don’t think I have ever been to a restaurant on Mother’s Day. Sounds horrible. LOL.