I'm also not sure why perl doesn't understand them. I suspect they must lead to parsing ambiguities - that usually seems to be the reason for such restrictions.

In any case, Perl does not have a history of disallowing things on the grounds of "readability" (that seems much more Python's style). What a person finds readable is very much determined by what they are used to, there really is no single perfect style.

Around 25 years ago I was working at Elsevier in Amsterdam, and once had a very heated discussion with the project lead when in code review he wanted to turn my mix of loops and map/grep pipelines (carefully curated so that no single construct was overly complex) into a single much more complex map/grep pipeline that to me seemed totally illegible. My line manager eventually explained that the lead had a functional programming background, and that I should look at the proposed change in that light. It took me a while, but eventually I got my head around it, and I'm now much more comfortable with that style (and find it perfectly legible when done right).