I think the cost of Lisp machines was the determining factor. Had it been ported to more operating systems earlier history could be different right now.
That was 40 years ago. If people wanted to program inside out with lots of nesting then unfold it in their head, they would have done it at some point a long time ago. It just isn't how people want to work.
People don't work in postfix notation either, even though it would be more direct to parse. What people feel is clearer is much more important.
It's not just Lisp, though. The prefix syntax was the original one when the concept of records/structs were first introduced in ALGOL-like languages - i.e. you'd have something like `name(manager(employee))` or `name OF manager OF employee`. Dot-syntax was introduced shortly after and very quickly won over.
People don't work in postfix notation either, even though it would be more direct to parse. What people feel is clearer is much more important.