This would require maintaining several versions of game servers, which would cost a lot. And people playing old versions tend to be people who don’t bring more money into the game, so it’s not profitable business.

Oh, except people like those who wanted, and got, Old School Runescape years ago. That’s a prime example of a product catering for people who liked the “old version” - except that people didn’t really want the old version as is, they just wanted to cherry-pick their updates. To take a comparable example from Conan Exiles, they would want to keep the old combat mechanics, but they’d still like to have the new dungeons and the new Purge, for example. In Runescape, this led to a point where the “old-school” version was receiving more updates than the “live” version.

And as I’m sure you can guess, the “Old School” Runescape still had the same monthly subscription fee as the “live” version, because the game company needed to cover the expenses of offering the version. So the only way Conan Exiles could have several versions would be to have a way to get money out of the players.

(I guess technically you could run an old version of Conan Exiles on a private server.)