The main problem isn't the arena.
Just an example. The DRG has one in storage. It just doesn't come out, because the cost transporting and setting it up is so that the DRG can't afford to use it without a sponsor/event organiser. And that has been proven to be a very fickle issue.

It's rather how many teams can build/rebuild a heavy twice a year?
And run non spinner events in between.