I don’t think that’s shady? When I was hiring contractors it was always project based with mutual understanding things could end quickly if the project or collaboration didn’t work out.
Yes, they get paid 1.5-2x, and that also prices in that it’s not always 100% utilization. Only once had a contractor oppose that, but that was in the context of (severe) underperformance.
In his case, the contract had something different, and they did not pay the actual invoice - that's the shady part.
With contractors, you have more freedom of choice when you write the contracts, but whatever contract you agree on, you still have to honor the contract as agreed.
Oh my bad, I thought you referenced contractors in general. In that case I agree: agreements are to be honored.