Now to add additional problems. 1000 tor nodes on a single platform would be very noticeable and geographically limited. Platforms also have different weight attached to them in the consensus, which adds further time requirements before a node is promoted. The developers do not want a single platform provider to be able to observe a large portion of all the traffic, so there are counter measures.
The attacker could try to create a handful of accounts on hundreds of platforms in as many countries as possible, assuming one verify that the platforms accepts tor and do not share underlying providers and data centers. The cost would then be the average price of said providers, which is going to be a fair bit more than the cheapest providers out there. Managing and spreading them out is also going to cost a lot of man hours. Also the secops need to be fairly on the point and need to be maintained quite strictly across all the providers.