‘User error’ is rarely a sufficient explanation for why something negative happens, particular when those users are professionals using a professional product. At some point one needs look at whether there is something in the product that causes those errors to happen or that doesn’t do enough to prevent them.
There's nothing inherent about Perl that causes people to use $z instead of $somethingDescriptive. And regexes have for quite some time allowed for insignificant whitespace to comment things in detail.
If you comment your regexes and use decent variable names, you solve 98% of the readability problems of Perl, and both of those could be enforced with a linter. But as I said, a lot of the problems come from one liners being slowly expanded. Using single letter var names for anything is fine in a one liner, but not good for long term program legibility or maintance in any language.
That's like the folks who say "the problem with C (buffer overflow, UB, etc.) isn't C, it's the people who write C". Which leads to at some point contemplative folks deciding either "this is happening so often, maybe it is the language" or "the majority of people writing this language are incompetent". While I've heard plenty of people in the C community espouse the latter view, having written C since K&R days, I think most people acknowledge it's a problematic language. But I don't have empirical evidence of a ratio.
I wrote a ton of Perl <=5 back in the day. I'm pretty sure I know why I thought it was a good idea at the time. I know where I fall on the above. I know why I, and virtually everyone I know professionally, don't solve problems in Perl any more. But hey...maybe I'm just incompetent.