The argument I can see is that 14 is the minimum feature set that every engineer knows how to use, and before 14 you are missing some of the "core" features of the language that are widely used today. By contrast, some things in 17 are still foreign to some engineers, although there are no real "breaking" changes from 14 to 17 (in terms of the model of how to think about the language). 20 and 23 are a bit of a mess in terms of support.