See this question.
Ideally we should be able to keep a tag, but flag it so that it can no longer be used. Failing that, however, we should just rename this tag so that it's clear that it's an old one.
Because every time we migrate a career-development question to Programmers.so, we piss someone off a little bit. It's annoying, even galling to find that what you thought was a perfectly good question has been migrated. Your first thought (unjustly, but nevertheless) is "WTF?!" It generates bad feeling. However justified the migration, making SO users unhappy is not really in our best interest, so we should try to minimise migrations.
And because migrating the questions is fire-fighting, not problem solving: it won't do a good job of stopping people adding new career-development questions. Neither will the message on the tag wiki, because no-one checks the description before adding the tag to their question.
Programmers all understand the word "deprecated", and the revised tag name would pop up as a suggestion when they type the old one, so they would see what was going on.