Question

Why would the Hawks play at a college arena?

They did not have a large enough fan base for a larger facility.
Their arena was not built yet.
The city refused to build them their own arena.
They wanted to train younger players.

Answer 1

The Hawks would play at a college arena is due to the city not letting them build their own arena. if that is not the answer I would go with their arena was not built yet.

Step-by-step explanation:

The fanbase and training has nothing to do, a arena can be filled by opponents fans and they can bring in more money more fans later on. So I would go with the city refused to build them their own arena.