I’m not on the payroll and one of the more prolific of plugin authors.
In my experience it is very hard to monetize plugin maintenance.
You can more easily get someone to pay for or sponsor the creation of a new plugin as a one off, but much harder to get someone to pay for the time for it’s ongoing fixes and support.
The biggest challenge is crowd-sourcing from the plugin users. You cannot make a living from voluntary donation.
Third party contribution to open source plugin repos is very unusual and most independent plugins are the work of one person.
It’s likely more straightforward for hosts like CDCK or Communiteq where clients are paying for hosting in any case and you can divert some of that revenue into plugin maintenance.
There is only one plugin (I’m aware of) that monetizes itself (Custom Wizard) outside of the major hosting companies. I co-wrote the infrastructure that was required to make that possible and the investment of time was significant.