Eh, I don't know. Part of what makes Dwarf Fortress unique is its meticulous attention to detail. Tarn has so far been able to concentrate so fully on the game's simulation aspects by mostly ignoring things like the UI and optimization.
Could he hire on another person to work on the non-simulation bits? Perhaps. But that takes money. Tarn makes donation information public, and he makes between $40k-50k a year before taxes and the ~$800 a month he pays his brother for the help he provides. Enough to support himself, but not nearly enough to hire on another full time person.
Not to mention there are already other games out there attempting to emulate Dwarf Fortress (Gnomoria and Towns immediately come to mind) in a more user friendly form, but neither of them yet come close to intricacy and scale of Dwarf Fortress.
If he opened up the code I'm sure people would do it for free. If he doesn't want to open up more of the code I bet there are scads of people who would do it for a cut of the profits. And yes if he doesn't improve things eventually a competitor will mop the floor with him.
Could he hire on another person to work on the non-simulation bits? Perhaps. But that takes money. Tarn makes donation information public, and he makes between $40k-50k a year before taxes and the ~$800 a month he pays his brother for the help he provides. Enough to support himself, but not nearly enough to hire on another full time person.
Not to mention there are already other games out there attempting to emulate Dwarf Fortress (Gnomoria and Towns immediately come to mind) in a more user friendly form, but neither of them yet come close to intricacy and scale of Dwarf Fortress.