Some of it I recognize as being an artefact of the time, when conciseness really mattered. But it's still obnoxious in 2025.
The whole thing reminds me of D&D, which is full of classes & spells that only exist in modern D&D because of One Guy who happened to be at the table with Gygax, who really wanted to be a wuxia guy he saw in a movie, or because he really wanted a spell to be applicable for that one night at the table, and now it's hard-coded into the game.
It was an artefact of bursting out of those constraints, but honoring them still. The roots of perl as a “more capable, less restrictive” sed/awk means that it must support `perl -pi.bak -e oneliner file`, just like sed did — and so from that core requirement forward, everything it did, does. By the heyday of Perl5 era, conciseness was not a requirement, but the sed-compat roots remained a focus of the language’s creator.