PimPamPet: I doubt it's a matter of them being unable to get copies of the missing games. It's probably due to licensing/compatibility problems that these alternate versions are prevented from getting a GOG release. Like ScummVM having problems with the SVGA Larry 6. Also, there is the simple fact that most people won't care which version of the game they are playing, only nerds on the internet do. :-)
I can guerantee you there are no 'compatibility' problems with any of these old games. They function on Dosbox just fine, and most function even better on SCUMMVM. Larry 6 Hires for example works fine in Dosbox. no old 16-bit windows required.
A few I mention function only on SCUMMVM or only on Dosbox though. But most have a program that they function on just fine.
As for PQ1 EGA and Space Quest VGA, and KQ SCI, there are many people complaining those are missing, considering they are practically completely different games, changed puzzles, completely different art, new and enhanced musical scores, new scripts, etc. There is a reason why the 2006 collections (that had missing games, were generally critically panned as far as 'collection' reviews are concerned).
And as of late, collections like Quest for Glory and this Larry collection have offered both the EGA and the VGA versions of the games.
Also may I remind you the Broken Sword fans wanted both the originals and the 'director's cuts' offered to them, and GOG gave them to them.