It's possible this was an ingenius land grab - we need the land for parking! oops, parking not necessary we'll build a hotel instead - but more likely it's just stupidity.
The problem is that rich important people who influence and make policy decisions are drivers. Normal people would think that this is New York, the stadium is on top of 8 thousand rail lines, and relatively few people are actually going to drive to a baseball stadium. Decisions about how much parking is needed are made by people who live in a world where people drive everywhere.
That's the world most people in this country live in, of course, but it isn't the world that most New Yorkers live in.