Why does modern Perl avoid UTF-8 by default?

I wonder why most modern solutions built using Perl don't enable UTF-8 by default. I understand there are many legacy problems for core Perl scripts, where it may break things. But, from my point of view, in the 21st century, big new projects (or projects with a big perspective) should make their software UTF-8 proof from scratch. Still I don't see it happening. For example, Moose enables strict a

[yyamano]

2011年時点でもこんなに複雑なのか。

[Yuichirou]

「なぜモダンPerlはUTF-8をデフォルトとするのを避けるのか?」 UTF-8を含むUnicodeというものの深淵。

[mad-p]

Perlでutf8をデフォルトにするための7つの手順by tchrist