Because you haven't submitted a pull request for it, of course.

As Pieter points out, it's not a two line change at all.

And although it would very much be a welcome feature I think you're overestimating it's usefulness. It's quite hard to hide the evidence of a second wallet on a partially encrypted system— shell history, log entries, etc would point to the location of another wallet. We have integrated encryption already for basic security, and the concept of a not-online wallet really requires the not online-wallet be actually not-online— trojans/malware/and compromises will _happily_ steal your displaced wallet when you _do_ access it, as it's absolutely trivial to just watch the bitcoin process and take whatever wallet it accesses.

I find the admonishment to use electrum in response to a message apparently concerned about security to be quite perplexing. Electrum is useful and interesting software, but it has a _much_ weaker security model.