Thanks to Uadjet, events are held weekly, and with good participation too. So clearly having something occur every week, at a set time, is not limiting its appeal, at least not in my opinion. What I believe is the problem with the market is that it attracts a low number of sellers with a limited, unvarying supply of goods. Hence people are not interested in attending because the products they can get are of no real value to them, not being unique or hard to find. That in turn limits the other appeal the market could have, as a place to RP on a regular schedule.
Unfortunately I have been unable to attend the market of late, but from what I recall, in the near past, peddlers of unique items or services, including GMs acting as engravers or offering items no NPC sells and no mob drops, would cause an apparent up-tick in player participation. Unfortunately such events were not announced in advance, I think that greater visibility would have further increased their effect on player count.
What could be done to improve the effect of the weekly market as an event would be to arrange for players (or GMs) to participate with original offerings, including games, shows or RP of special types of participants: I did some skill games in the past, and I have seen players RP reporters, bards, fortune tellers or even pickpockets in the market with fairly good results.
That sort of actions could be of great help, but just being there for the market would be a start. And that, I know, is an advice I should heed myself.