DF has been around, and under active development, for ten years and is quite a bit more popular than you seem to realize.
> If he doesn't want to do it himself he should let someone talented in that area join the development team.
And it's also one guy living off Patreon and the donations generated by DF. Where should he find the money to pay an employee?
Kickstarter for Dwarf Fortress graphics initially, then Patreon again with an expanded community due to the Kickstarter. Seems like that would work reasonably well, without changing the basic game.
I've read the developer's reasons for not having graphics, and it's BS. If he doesn't want to do it himself he should let someone talented in that area join the development team.
You're right of course, it's his project and he doesn't have to share it. It's free and beggars can't be choosers. But a game belongs as much to it's community of players as it does to the people who create it. The best games ever created have all been open, either open source or by embracing a modding community. As a gamer who's had a passion for all forms of gaming since before I could read, I find the developer's attitude extraordinarily negative in general.
That's my opinion, nobody is obligated to share it. I'm just saying something superior is going to come along and when it does nobody will remember DF. And that would be a shame, really.