It very much isn't a hail Mary to generate money, they'd have bent over backwards if they'd wanted to keep big players like Apollo and RIF on board, if it had been a hail Mary. 20 million bucks a year is nothing to be sneezed at.
The fact that they left Apollo out to dry shows that it never was about making more revenue, but rather to stamp out competition for their own app. As soon as it has accessibility parity with other apps, it'll turn off API access for unofficial reddit apps alltogether.