They don't even have to provide much (or at all) financial incentive for miners, as for them there is no downside in adding another blockchain to hash. It only needs to be for something a big part of miners would support for one reason or another, and you get your hashing power.
The downside would be the disk space and bandwidth required to maintain new chains. If what one is able to mine isn't valuable enough to pay for those costs then most people would not support that chain with hashing power.