A couple of reasons.
It restricts you from holding events which require a 250m track. It isn't like the USA is overrun with indoor tracks so you can chose another venue.
Sub optimal as a training centre for Eastern State cyclists. Although there can be slight differences even in 250m tracks, since the World Championships must be held on 250 tracks it would be optimal for elite athletes to have a venue which rides similar to venues they will race on overseas.