The developer thinks maybe they can make this work. Maybe there's a combination of a lower limit of API calls and an upper limit of what people are willing to pay for their app that will let them keep going.
The developer's lawyer recommended that to sue reddit for destroying their livelihood they would need to demonstrate that they had tries with the new system and it wasn't feasible in order to make their case stronger
The developer wants to take advantage of the third party landscape being just them now
Personally I think the first one is the most likely. It seems naive and bound for failure. But its also the least conspiracy theory and doesn't assume malice