Because its faster at OO than Perl 5 and has a tonne of other builtins that make it easier to write algorithmically performant code. Not to mention its trivial to write parallel code. I dont think there have been any optimisations in the regex engine in the time you're discussing. The raw IO however has seen huge improvement, especially if you state you arent using unicode and don't want grapheme normalisation. In 2011 just my tests took 35s to execute. Now that's 1s and startup time is 2/3 of that. Something like CSV parsing or even log parsing where you split instead of regex is competitive. Last I checked faster than Ruby but slower than C. But yeah you do still have to work around the slow bits, or be explicit with what you want like ascii IO.
Faster OO but dog slow regexes? This is Perl, right? The Practical Extraction and Reporting Language where extraction is largely the work of regular expressions and, now, grammars. OO languages are a dime a dozen so how can OO be Perl 6's main priority?
To be fair Perl 6 returns structured data from regexes, whereas Perl 5 returns flat data. That has huge implications on how different the regex sub-languages gets parsed. It also has a significantly different syntax, and integrates more into the rest of the language. Basically it had to be created from scratch, so that would mean that it couldn't benefit from the already existing optimizations of the Perl 5 regex engine.
Perl 6 is also a mostly unpaid volunteer effort. So everybody gets to choose what they work on, and very few people are brave enough to work on that aspect of the compiler.
Also I would say that the main priority of Perl 6 is to integrate many ideas from many languages and bring them together in such a way that it seems as if all of these ideas always belonged together.
The reason why the object system sees more optimizations is because everything is, or can be seen as, an object. A big improvement there, can for example make regexes faster.
