First, yes, there are reasons to have the various versions. 2005 can open DTS, for instance.
But this is what I get when I use "choose default program" with .SQL files. Big hugs to Microsoft for never including the version number of SSMS in there. It makes it lots of fun when I wind up accidentally resetting it.
Putting it in here so hopefully I won't have to do this 10-minute exercise next time.
Top left: 2005
Middle left: 2014
Bottom left (highlighted): 2016 CTP2
Middle right: 2012
Bottom right: 2008 R2