R is also far more popular than Lisp. According to TIOBE: https://www.tiobe.com/tiobe-index/ R is #15 (1.06%), Lisp is #26 (0.54%).

So the existence of R is evidence that Lisp's syntax is a serious problem. If a language providing syntactic sugar has a significantly increased adoption rate, that suggests that the bitter pill of your syntax is a problem :-).

Language adoption is a complicated story. Many Lispers won't agree with me anyway. But I do think the poor uptake of Lisp demands an explanation. Its capabilities are strong, so that's not it. Its lack of syntactic sugar is, to me, the obvious primary cause.