Lots of gyms don't anchor their equipment - I've seen it lots of time. They may do it for lease reasons but I'm guessing it's convenience also - once you bolt something down, you cannot move equipment as easily. I'd say the risk from something not being bolted into the floor is dependent on the type of equipment it is.
We can't predict the future; you can leave something like that and nothing might not ever happen. But if it does, and it's not bolted, and the injury was caused from the equipment being unsecured, then the gym will likely be responsible.
That said, I think there are bigger risks in the gym that an owner can avoid, like making sure to have a defib unit, having someone trained to use it and otherwise trained in CPR and making sure equipment is in good working condition free from wear and tear by conducting regular inspections and making sure to replace worn parts timely.
Keeping the floor areas clean, clear and free from hazards and defects would be big too. A gym owner probably has more exposure to a slip and fall in the bathroom than he does to a machine tipping over.
But if it were me, I'd probably bolt them down - people do some dumb shit and doing dumb shit is not necessarily a bar to recovery for a claim