First, we do have careers (and also education, learning, academia, and phd). It's not a particularly popular tag here, as you can see. It may not always be applied where it should (e.g., Things to consider about masters programs in statistics), but we're not especially zealous about retagging old questions here (see Retagging old questions for more nuanced discussion).
I agree with @gung that an advice tag sounds overly ambiguous. I'm not sure what it would add to organize questions this way, and also wonder whether it's really doing math.SE any major favors. Feel free to pitch it to us if you think it has worked over there, but popularity isn't necessarily an indication of practical utility. It seems particularly fishy to me that its tag wiki suggests using another tag too, but hasn't been filled out much at all yet – not even to disambiguate it from the other, the soft-question tag.
As for that tag, I agree it could be misunderstood or misapplied as pejorative derogation of a question's scientific merit, but tags are misapplied often enough (gung had to correct me on my own use!) that I prefer to accept this as par for the course and worry more about the intended meaning of the tag. There's still plenty to worry about there. First, you've got another excerpt-only tag wiki there, so its use doesn't seem very clear to begin with – not exactly a strong candidate to nominate over here...Second, "questions that don't admit a definitive answer" reminds me a lot of the Help Center's don't-ask page, as well as the
too broad text – "There are either too many possible answers..." – and the
primarily opinion-based text for closing questions:
Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise.
I'm concerned that a soft-question tag would legitimize questions that test these boundaries. Maybe this wouldn't be a bad thing; the questions could help define the boundaries, and the tag could help mark boundary cases, but this begins to approach the dangerous, implicative, prejudicial territory again.
Third, I echo @Glen_b's observation that it's quite a subjective call as to when one should expect a definitive answer. Since statistics often entails a considerable amount of error tolerance and choice of competing models, definitive answers may be somewhat rarer here than on Mathematics. I would prefer not to see questions organized by this characteristic, but by its opposite (proof, I assume) wherever a definitive answer is clearly necessary. IMO, if the idea of a soft-question tag is to encourage less-than-definitive answers, the place to do that is in the body of the question, not in the list of tags.
BTW, I downvoted too for these reasons, but to echo gung once more, it's not because I found your question useless or unclear! As a matter of fact, I just retagged a new question with careers thanks to having that tag brought to my attention...so thanks for asking anyway!