Because "Early 80s DOS games" and "DOS games" is not necessarily the same thing. In the early 80s (around 1983/84), those games came as auto-booting 5.25'' floppy disks (commonly called "booters") for the CGA (rarely: EGA) graphics adapter.
In fact only a small number of them deserved to be put into the "DOS games" category, since they had their own bootloader that circumvented the built-in OS (like much more widely known on the Amiga later). Don't imagine that there was any AUTOEXEC.BAT running an .exe file or anything of that sort.

Besides, in Seiya's "MS-DOS Goldies" thread, the games referred there may be called 2nd (or even 3rd) generation for a reason! For that was way, WAY later...
There are not many emulators around that can run these "booters". Flopper is one of them, and I also managed to run lots of them using MESS (Multi Emulator Super System).
So I'd be interested if somebody has started making a GameBase from these early classics.