Revealing manuscript referees' identities after review: Why is this a bad idea? Motivated by the How can an author get assurance that his work will not be stolen by journal staff or reviewers? question:

Authors submit their manuscripts to be reviewed by a journal or conference. Unless the submission is double-blind, the authors' names are listed on the submission, so the referees know who the authors are. Anonymizing referees during a review makes sense, since, for example, you don't want the authors contacting the referees while they are performing the review of the manuscript. But what about after the review has taken place?


  Why don't journals and conferences make available to authors the names
  of the referees who have reviewed the manuscript?


It really makes no sense to me. 

Other questions on this site related to the present question:

What to do if a referee plagiarises the result after rejecting a paper?

Are the referees of a journal allowed to reveal the title of the papers they review after the review process?

(And there seem to be many more related questions...)

One common gripe in related questions seems to be the worry that referees can "steal" ideas presented in manuscripts. (I've personally not worried about this at all in my previous submissions.) A possible tactic to thwart "idea-stealing" is to post the manuscript on a pre-print server (e.g., arXiv); however, not all fields/sub-fields think it is kosher to do this. 

Thus, given that the "post-manuscript-on-arXiv" solution is not applicable to everyone, this question seeks to determine what are the main, logical reasons why referees' identities are not revealed to authors post-manuscript review.
Note that I can see pros and cons of optionally permitting reviewers to disclose their identity, or even making peer review completely transparent. But the following focuses on the problems of disclosing reviewer identity after a decision has been made about the manuscript.

It creates a conflict of interest for the reviewer.
There is an incentive to provide a more positive review. For example, there is the possibility that the author may be more positively disposed to the reviewer in the future, if the reviewer provides a positive review. Also, the reviewer may not want to damage an existing relationship.

There is little difference between perceived conflict of interest and an actual conflict of interest. Thus, even if the reviewers are not influenced by this disclosure, others evaluating the integrity of the publication may perceive a problem. 

It can create more work for the reviewer. If a reviewer knows their identity will be disclosed, they may have to spend more time being tactful. It's hard enough getting reviewers, if the workload of every review increases because the reviewer has to spend more time being tactful or worrying about the consequences of their review on their reputation, then this may make it even harder to find reviewers.