To be compatible with all kinds of testing or other fixed states of a game without overwriting neighbour clients with a different api version please allow addon authors to keep seperate trees of updates within an addon.
Addons on a testing server might use newer api then the live realm,
Addons on a oldschool classic realm might need other api calls.
If you mix them up, they break.
Older addons can still work on new game version, but probably not the other way around.