There are different considerations for generally improving tagging on a question vs. cleaning up a deprecated tag.
Organized Tag Cleanup
Cleaning a deprecated tag is for the purpose of site maintenance. It ends up bumping old questions, largely with no benefit to most of the questions, but that's a side effect of the process.
The period during which a user is below 2K rep is intended to provide for learning the ropes as to what makes a good post. Edits to improve posts are reviewed to provide feedback and to avoid bad edits degrading a post. The system doesn't distinguish edits by their purpose, so <2K users are able to engage in site maintenance kinds of edits, but that's not a good use of anyone's time.
Tag cleanup efforts can be performed efficiently by users with edit privileges (2K+, and it's even simpler at 10K+ because tags can be changed without even going through the edit process). When users <2K do it, it creates a review task for two to three users who have the rep to simply do the cleanup themselves, so the cleanup requires three to four times the effort, and doesn't really contribute to the learning process.
Many reviewers don't follow the questions raised on Meta, so they may not be familiar with the tag cleanup efforts. If a <2K user engages in tag cleanup, and doesn't reference the relevant Meta question, the proposed edit is likely to be viewed in the context of a question improvement. For the majority of affected questions, this site maintenance isn't really an improvement for the question, so the edit might be rejected.
Question Improvement
Editing just to improve the tags for the benefit of the question should serve one of two purposes: help it attract answers and/or help people with a similar problem find answers.
If the existing tags are seriously problematic, we can improve either case by creating better tags, defining them with at least wiki excerpts, and retagging all of the affected questions so the tag's proper use is the rule on all of those questions rather than the exception.
New tags don't have followers. A following develops later if the tag serves it function. So tag improvement is more of an investment than an immediate benefit to those questions. No matter how good a tag is, if it is not used on most of the applicable questions, it just provides decoration without serving its intended purpose.
A tag can be critical to answering a question. For example, if the problem or solution depends on the OS or particular software or hardware, lack of a tag is substantive. Just adding that tag is likely to justify approval of an edit as long as there aren't numerous other problems that aren't fixed in the process.
But if the tag information is already covered in the question and the question is already adequately tagged, adding a supplementary tag as the only change is likely to be seen by a reviewer as not a substantive improvement. Even there, on a brand new question, if there is a chance that the additional tag might help attract answers, a reviewer might approve it, but likely wouldn't approve it as the only change to an old, inactive question. Bumping a question so that it can go back to being buried with better tags isn't really an improvement.
Another consideration is tag bloat. Many of our tags either don't serve an important tag function, or are one of many similar tags that are inconsistently used. A new tag even gets deleted by the system if at least one more question isn't tagged with it in 6 months. So if the edit consists of just a new tag, and it isn't obvious how that tag improves the question, the reviewer may see it as not a substantive improvement.
Linked Threads in the Question
The first linked thread proposed replacing the Mikrotik tag. In that question, there doesn't appear to be anything specific to Mikrotik that would affect the answer. The manufacturer tag decorated the question because that happened to be the hardware brand. Cleaning up the manufacturer tag in this case is best accomplished by removing the superfluous tag.
The second linked thread proposed adding a tag. The OP had commented "I don't think it's hardware related". So the proposed tag doesn't appear to serve an important tag function. As the only proposed change, it was not an improvement.
In the third linked thread, you proposed replacing the [asterisk] tag with [freepbx]. That would definitely not be an improvement, so rejection on that basis makes sense.
You subsequently proposed removing the [networking] tag and adding the [freepbx] tag, which was approved. That change wasn't actively harmful. It included correcting the reference to the screenshot, and perhaps the addition of [freepbx] might be useful. If the edit had been just the tag change, it might well have been considered too inconsequential; but it was combined with a correction in the body of the question.
