They aren't delivering the service for which they are being paid for

If you contract somebody to paint a house every month for 12 months, and the house burns down after 6 months, chances are you wont have to pay them out (depending on the wording of the contract). Even things like Foxtel or Telstra have contract termination fees but never the full amount

I'm a contractor and I have very clear wording in my main bread bringer contract that if the agency no longer requires my services they can suspend me or cut back the work. If the people I work for have to close down as a result of the virus, which is very likely, I wont continue to get paid

No different for players (unless there was a severe oversight by those who wrote the contract thinking something like this would never happen so might as well save the ink writing it)

The players aren't playing. They aren't delivering the service they are being paid for - regardless of the circumstances. They are in breach