PHP never stood out as a language with very clean syntax. It is very PHPesque to put the burden on the user of the language instead of going the extra mile and implement something that might be harder to parse, but would be more consistent. Inonsistency in general is one of PHP's issues.

if you ever had the misfortune of seeing the code for the parser and lexer of earlier versions of PHP youd see that it wasnt due to parsing simplicity but rather the author making poor syntax decisions due to a lack of understanding.

Then being walled in by backwards compatibility

Interesting, but not surprising for a language where functions were "hashed" as their identifier's string length. Do you have a link?

I do not, it'll be in whatever version control php is in though I'm sure.

Another absolute horror parser was the wikipedia wikitext parser. An ambiguous hand written mess of epic disgust.