I mean, in Lisp everything is S-expression based. That this models the tree structure of HTML documents is convenient and not entirely coincidental (SGML, plus the deep truth that trees are fundamental to structure, and S-expressions being the language in which The Word was spoken and all)

But if we were talking about outputting CSV data you wouldn’t be able to say

In lisp the templating systems are S-expression based instead of string interpolation based, which at least models the tabular structure of CSV documents

Because hierarchies don’t model tables especially well.

So the suitability of lisp for outputting HTML feels slightly coincidental.