Influence. A completely amazing amount of Java was written (is being written) and there's a huge workforce in that language.
I think that it's possible if say Gosling hated + concatenating and had provided Java with a different String concatenate (it clearly wants a concatenate operator, but it needn't be named +) we'd see that popularised and while some languages with overloading might overload + it wouldn't be ubiquitous. I can't prove that of course, it's purely my opinion.
Huh. I'm pretty sure that at least some BASIC dialects I used did not have concatenation, but you seem to be correct that in general they did. This intrigued me enough to go dig through nested "from old machine" directories until I found some BASIC (I'm going to guess that I have not written any BASIC since about 1992) and you're correct that BASIC from the era which didn't live on cassette tape and thus I still own does have concatenating + operators in it.
