Well that's part of the problem. The funny thing is people (like you) think that more money means faster development.
And based on that assumption they feel they can make the argument more money = faster development.
This isn't necessary the case. The only thing that more money could bring is maybe faster renders. That's only one part of developing a game. And the render process itself can usually done in batches. Setting up a scene and everything around it takes a lot more time then the actually rendering would be my guess.
Writing goes faster with more money? Nope.
Posing and setting the scene goes faster with money? Nope it doesn't
Does money make the creative process go faster? nope.
If someone earns enough they might hire some people to do stuff for them, but that comes with a half of dozen other potential problems.
People ( like you ) are actually wrong assuming that money can't equal faster release's. It actually can via motivation.
In this case the project happens to be a hobby or something the dev does once in awhile. Dev is content with what he's setup here. He isn't actually trying to get updates done.
I bet if we look back at his release schedule in the beginning he was much faster. He was motivated by money to get content out, now he's just doing whatever and could care less.