It would be another release, so they just need another agreement with Revolution. To get the original to work on modern systems is also not a big problem, it runs ScummVM. In my eyes it's not a question to choose between both versions here on gog, they could without any problem sell both versions. It would be very similar like the first Myst game. You can get the original Masterpiece Edition and the remake Real Myst. They have both the same story, but reviews say they are diffrenet enough to play both (if you interested in the series, of course).

I assume they thought the DC would sell better, and hey, they were probably right. I would like to see the original version on here though.