Could you say a bit more about that? Normally I think "have to support people stuck on old versions" is something that happens when you're selling enterprise software to insurance companies. This is the first I've heard of it in games.
As mentioned, some versions of the game introduce breaking concepts that earlier players may not want to deal with (either because it breaks save compatibility, or they don't like the mechanic, etc).
Minecraft has this somewhat also, with some people sticking on various versions because of mods, or play style, or combat, etc.
For example, one huge change was going from a 2D map to a 3D one, another was how world generation was done.
See "Eras" here for the big ones: https://dwarffortresswiki.org/index.php/Release_information
This actually used to be the norm: you'd release slowly, and support old versions for years (which still isn't that long, all things considered). It wasn't until relatively recently that six months became some sort of unconscionable amount of time to support software, because it's friendlier to the companies and developers writing it, instead of the users using it.
Players comfortable with the ASCII graphics version (the one that existed for years) often just paid for Steam release with pretty graphics just to support the brothers. And then kept playing the "hardcore" version they are used to.
On the Steam platform for instance there is an option (perhaps developer supported) to stay on a certain version of a game. For instance, in the game Mount and Blade: Bannerlord, players notoriously stay 2, 3, or even 10 versions behind in order to maintain compatibility with specific mods or sets of mods (10s or 100s of mods). Eventually, enough of the modders move to the next or latest version and the players gradually move with them.
Games with "always on" or auto-updaters avoid this.
DF had a massive update probably a decade or more ago that changed the game from 2D to 3D (still represented as 2D z-levels though). With such a change, obviously some people would want to stick with the old version. There have been numerous large updates since then (the game has been in development for 22 years) and with each you get some people that just don’t want to update, either because it might ruin their current games or they prefer to avoid new features etc.
Another example is the various Dungeon and Dragons wikis that allow you to toggle between versions, since it has existed for 50 years now.