The journal sidebar module only lists the most popular tags because of performance limitations -- the query to get the whole list of tags, with usage counts, is enough of a database hit that we can't put it on the main journal page or the reading page where the full list would get loaded every time someone looked at their recent entries or their reading page even if they weren't specifically looking for the full tag list. However! The "Most Popular Tags" heading is a link to the full /tag page, where (since people generally load it way less often and only when they're explicitly looking for tag info) we can list everything. So: nope, we can't show the whole list there, but we have at least made it easy to get to the full list.