That’s weird. Maybe @cgrunenberg can shed some light on that. But apparently others have run into the same problem: Can't log name of record via Smart Rule Script
So one is basically out of luck with Reg Exes in smart rules: neither JavaScript nor ObjCAppleScript are usable.
OT: I agree that Perl is more powerful re Reg Exes, but for me nowadays, JS is good enough. And it is a bit more legible than Perl 