you are also betting they do not have a natural disaster.
you are betting power costs don’t shift bigly
you are betting the country that hosues the gear does not shut power off.
For viabtc, the above points are likely less worthy of any consideration, but the point you mentioned here is key
so if you buy a contract you are betting that the contract does not get too good
I have noticed and warned about this subject back in November 2020, Viabtc will only allow you to point those contracts to their PPS+ pool, which is more than clear that Viabtc does not really own any mining gears, they will simply collect cash from you and give you bitcoin based on the theoretical income of that imaginary hashrate you pay for, so once the contact starts generating a lot more than what you pay, I don't see what stops Viabtc from rejecting to pay you anything.
Given that they are a well-built company, they won't just scam you, they will probably offer you a refund and maybe some kind of bonus on top and tell you "sorry our mining facilities were shut down by the government" or any other excuse, they could be honest and bear the loses, but I highly doubt that they will pay you a 100$ in
BTC in return for say for an example the $20 you pay them, this is just a high risk that I certainly wouldn't want to take under any circumstances.