The merchant job is something that spawns based on a coin toss, if you are lucky, you will spawn in three times in a row and get to enjoy it, if not, you will leave frustrated because RNGesus thinks today is not your day.
I think it's kinda silly, and I'll set out my very dumb reasons as to why:
For one, it's really frustrating, imagine having the captain role spawn only after a coin toss, or warden, or quartermaster, or chemist, or and or and or, if you wanted to play a round as any of those jobs, wouldn't it be frustrating to hear the "Welcome to Space station 13!" ring out and you are left with the main menu staring you right in your face? "Oops, choose something else now!"
Two, it's pointless. The merchant as is, is very RNGish in it's nature, sometimes the stuff you can get will be game changing for an antag equipped with a decent amount of cash, but a lot of the times your stuff is more useful for the crew, at times, you get basically nothing in terms of decent merch to sell, it's all a game of dice as to what you get, who wants to buy, and most importantly, what round it is.
An antag may want to buy your guns, sure, but don't forget that security may also want to buy your fancy stuff, and out of the impressive two times someone wanted to purchase arms from me, one of them was a departmental purchase.
Now, third point, time. Setting up your ship with various bits and pieces to sell takes time, trading with NPC traders to get better stuff takes time, and a lot of it, from what I've seen, traders tend to arrive at least 40 minutes after round start, with me it usually takes a hour, because you want to sift through all the stuff you go, take out the good, then put it up, and maybe do some minor ship adjustments.
By the time you might get to Aurora, it could be too dangerous to dock with it, so the merchant will have to juggle whether or not to dock, by the time the merchant does dock, a traitor would probably already have all they need, if not, well, the merchant might not have what they need, so it's just RNG on RNG on RNG.
You might not even know there is a merchant to plan around them, since they don't show up on the crew manifest (no duh), and the only knowledge of them you'll have is what they give you, when they give you. Again, time and RNG.
Final point, that being, having a merchant all the time doesn't make sense since Aurora isn't a trading hub! Well, for one, merchants won't be on all the time, since not many players choose that role every single round, second, Aurora is a:
A - A mining station, a phoron mining station no less, with plenty of goodies to trade.
B - A research station, if resources weren't enough to have ships docking with it, the various fancy stuff that Aurora produces behind those closed science airlocks definitely will, since fancy gadgets that do little useful will interest many people still, especially One of a kind!™ gadgets.
And the same could be said about antags, it's a game.
Edit: Courtesy of Chada, Jade and Happy_Fox, issues plus solutions.
Issue 1: The Merchant is currently limited to create novelty on the role. (We want it to be more common)
Issue 2: The Merchant is also limited to prevent player culture forming around aiding security / antagonists and to artificially create tension in crisis' aboard the station, which its' shuttle makes it hard to do
Possible solutions:
Solution 1 (For issue 1): Make the Merchant 100% common on Extended, and just raise the RNG on secret to keep the novelty but make it more common.
Solution 2 (For 1 - 2): Remove the limitation and instead randomly limit the selection of round-start items for the merchant.
Solution 3 (For 2 - 1): Make merchant no longer able to be an antagonist role or put more emphasis on it being neutral in station conflicts.
Solution 4 (For issue 2): Lock the Merchant shuttle on code red, make the merchant shuttle clamped to the station, give the merchant a bluespace override that rips apart a piece of the shuttle in return for an escape.