@duerer I am not completely sure, I think it has partially to do with the fact that these Addons are made by the Community and when they would be in the source code, they would have to be maintained by Blender developers…also the size of the source is taken into consideration, I think.
As to what is on by default, that is obviously: as little as possible…I am pretty sure that for instance @waylow never uses F2 or LoopTools.
Personally I think this system works great; I enable the Addons that I always use once and then forget about it. (I can imagine that it’s a bit of a nuisance when you are making tutorials and every time must tell people to enable the Node Wrangler for instance…) There are a few that I only enable when I need them and then there are many that I never use and quite a few that I have never tried and do not know what they do. External free Addons I use very rarely, because very often they get abandoned at some point.
