People write games for DOS emulators (especially DOSBox). Mostly mods of existing DOS games (our son loves Commander Keen mods), but more rarely new from scratch games as well.
However, the problem with developing games/mods for an emulator such as DOSBox, is you may find they run fine in the emulator but don't work in real DOS. Some years ago, I had MS-DOS 6.22 running under VirtualBox and our son was using that to play DOS games. He wanted to play this Command Keen mod he saw on YouTube, but it kept on crashing with an "out of memory" error. Eventually we tried it on DOSBox instead, there it worked. I tried to free up memory by tinkering with CONFIG.SYS/etc, but it appears to be impossible to get that much free conventional memory with real MS-DOS, even when making fullest possible use of UMBs and the HMA. I never tried FreeDOS, but it might have the same issue.
However, the problem with developing games/mods for an emulator such as DOSBox, is you may find they run fine in the emulator but don't work in real DOS. Some years ago, I had MS-DOS 6.22 running under VirtualBox and our son was using that to play DOS games. He wanted to play this Command Keen mod he saw on YouTube, but it kept on crashing with an "out of memory" error. Eventually we tried it on DOSBox instead, there it worked. I tried to free up memory by tinkering with CONFIG.SYS/etc, but it appears to be impossible to get that much free conventional memory with real MS-DOS, even when making fullest possible use of UMBs and the HMA. I never tried FreeDOS, but it might have the same issue.