I realize some of the later titles might involve more complex emulation, but surely some of these titles are just DosBox shells. Is it just because they're all sold as one, even though you download them separately?

GOG frequently refuses to list non-Windows platforms if the game is not natively available for the listed platform. The DOSBox-based Might&Magic games should work fine on any well-configured DOSBox, regardless of host platform. I played World of Xeen via a Linux-hosted DOSBox.

In my experience, the Windows-only offline installer runs fine under Wine, and lays out the files in a way that I can then use a Linux-hosted DOSBox to play the game. That is what I did for World of Xeen. No "real Windows" systems were involved. Yes, it is a nuisance, and it would be nice if GOG offered a proper zip bundle for games where the "install" process is just dumping a bunch of files on disk, with no need for registry entries. That method wouldn't be able to show advertisements for GOG games I don't want, though.

You can also use innoextract. In fact, that's what I did to install World of Xeen in a very unusual environment; under termux on an Android phone.

Some details for the curious (or those who want to try it themselves):
* termux from F-Droid (don't get the Play Store version)
* Add the x11 repo to termux
* A VNC viewer app is also installed on the phone
* Packages installed under termux: the tigervnc server, innoextract, and DOSBox.
* I did have to run the Darkside installer, then copy the files (including DARK.CC) to the main directory before the game would run
* Sure enough, the game runs (with sound, even) on the Android phone after doing this

This should also allow for installing the game on a Raspberry Pi, though you don't need the termux and VNC stuff there; just DOSBOX and innoextract

innoextract is your friend, and may even be packaged sufficiently well by your distro. The fact is, as long as there is at least one Windows binary (MM6 in this case), gog will never release a "Linux" version. There are, of course, other games, without any Windows binaries, and gog still won't release "Linux" versions, but maybe you could at least convince them otherwise in those cases.

Converting the dosbox config is usually trivial, even if it involves changing CD config files and paths. Usually you just need to make a few path changes in the config file, and disable the overlay (used for cloud saves, not supported w/o Galaxy anyway). Coincidentally, a quick check of my notes says that CD config was, indeed, broken for mm4-5: ..which basically just involved converting backslashes to forward slashes.

Of course, I have enough dosbox games to have taken steps to make that sort of thing almost automatic, I guess. Here's my entire woxeen config file, for example: Yes, it's more effort to get it working on Linux than on Windows. What do you expect from a Windows-focused store?

Edit: right after posting, I see now that there is a gap between my response and the last post, probably due to a filtered user. If that filtered user already answered your question more completely than I, I apologize. I won't unfilter to see what the response actually was, though.