Frankly, it's self-indulgence. Recently, Stallman has been complaining about the diversion of resources away from free software towards retro computing.
RMS confuses the symptom for the disease. Retrocomputing is almost always pure hobby, done for joy and recreation, while there is plenty of drudgery in libre/open source software. He shouldn't be surprised when geeky goofing off is a lot more fun for people than frequently unpaid labour.
As much as I hate to give Stallman oxygen, as a fellow retro computing enthusiast I'm morbidly curious to read about it. Is there anywhere I can find the full text of his caustic remarks?