I expect that this is not an oversight, but is rather part of the Perl philosophy.
Think again. Since the time that Perl 5 came out, not over 10 years ago, maybe one or two new keywords have been added to the language, pos
being one of them. For the rest, we are stuck with what was in it from the days of Perl 4. And in those days, there were no modules, and definitely no loadable dynamic extensions, so either something was in the language, or you had to write it in Pure Perl. (Or you had to build a special customized Perl binary, like OraPerl
As a result, there's quite a few of rarely used keywords in the kernel, like gethostbyname which didn't even get its own private entry in perlfunc, while ordinary others like cwd are strangely missing. I'm quite sure that, if they didn't care about backward compatibility, a lot of those old keywords would be kicked out into their own module, such as the oddball functions related to sockets: connect, accept, bind, listen, recv, send, and a couple of even more obscure ones. It's only because perl 4 had them (and had to have them, if you wanted to allow people to write network software in plain Perl), that they're in the language.
These days, if people want a new keyword, they just ave to write a module (or an XS module, if it has to run very fast). For most applications, that suffices. That's why in the last 10 years only a few new keywords have effectively been added — keywords that likely couldn't have been added to the language in any other way. Like pos.