I do agree that the suggested synonyms page could use better visibility. Maybe a task as part of the review queues.
That said, I don't necessarily agree with some of the suggestions. They may be languishing because nobody else agrees with them. Or, the questions under the tag may need to be reviewed and evaluated before the synonym is actually created.
I'll just give one example.
google-maps-markers <-- marker
This is an example of co-opting a general term "marker," and using it for a more specific meaning. These kinds of synonyms exist because attaching it to a more specific tag either causes them to use the more specific meaning, or abandon the tag altogether.
Well, marker actually has a tag wiki that says that the tag means Google Maps Markers, and most of the questions actually refer to Google Maps. Even markers (which has no tag wiki) also almost exclusively refers to Google Maps questions, which is kind of amazing, actually, for a generic word. So far, so good.
But closer examination reveals that the tags for this subject are a bit of a mess. Many of the questions tagged with [marker] or [markers] also use the map tag, which is a data structure, not "A diagrammatic representation of an area of land or sea showing physical features" (that meaning is ascribed to the maps tag). Not surprisingly, many of these questions also have marginally useful tags such as zoom, search, fragment, and item.
Creating tag synonyms combines the tags into a single list, which can make it more difficult to find these kinds of problems and fix them first.