AaronOfBarbaria
Adventurer
I don't consider not having time to do more than one campaign but being willing for that that singular campaign to be any of a number of games/versions and not being willing to run/play anything but a singular game/version to be the same thing.Well, in fairness one other thing (and I'd hazard a guess the most common thing) that can force a mutually exclusive decision is sheer availability of time.
If a DM only has time to run one campaign she (and her group) have to choose what system it'll be using; with the choice of one by extension thus excluding all others. She might be quite happy to run 5e, or 1e, or 3e; but she only has time for one of them and once one is chosen that's it for that campaign.
Lanefan
For example, I only have the time to gather all my preferred players once weekly, so we alternate D&D 5th edition and Shadowrun 5th edition in that scheduled session - and we have more D&D 5th edition campaigns, and campaigns of other game lines (Exalted, Call of Cthulhu, etc.) waiting to fill in once one of the currently running campaigns reaches its conclusion, plus I am willing to run other versions of D&D and other D&D-like games (Dungeon Crawl Classics, Adventurer Conqueror King System, etc.) but my players prefer D&D 5th edition over those.
Which is markedly different from if I were to say "We can only play on Friday nights because of our schedules, and also we can only play specifically D&D 5th edition because I refuse all other versions of D&D and also all other table-top role-playing games."