Originally the idea of BOINC was, to provide huge amounts of computing power for science projects that otherwise could not afford to get this computing power, like by renting supercomputer time or so. That did not include commercial projects, who just try to do things cheaply and make more profit that way.
The motivation (for me and most other, I guess) used to be some feeling of pride, to be part of a important science work. Like finding gravitational waves, or climate change, or dangerous asteroids. Or, at the beginning, finding alien communication.
I never expected to get payed for this. But of course it would be additional motivation, and help to cover some of the cost running BOINC.
If it would work similar to Steemit, rewarding processed work units, it would sure boost the participation. I guess it could be done somehow.