It's just a hard thing to implement. Since anyone can access /stocks in the same way, there's not quite the need for a stock broker like there is irl.
But let's assume there was a Stock Broker job made. How would it work?
Things like miner are quite obvious in how the money & xp is gained. Break X block(s), get X amount of $$ and XP per block broken. Simple.
The realtor is a little less direct in how they make money, i.e. their income doesn't come immediately after they put forth input. They take the action of buying the house, but don't necessarily get X amount for buying and whatever they will make in profit comes later, at the consumer's discretion. To make the realtor job worth getting, they are allowed extra access in the form of /find and an increased plot limit.
Now let's think about the Stock Broker. With the aforementioned jobs, this new job could go one of two ways. Either the Broker gets income directly based on their actions or they don't & get extra access instead.
Direct: In my opinion this wouldn't work from a mechanics standpoint. Getting a set amount of money/XP per trade is too easy to abuse, especially since there are times when the stock market is closed and prices don't change. Buy at $5 ea. just to turn around and sell it for $5 ea. for $$ and XP? Too easy, free money. Even if there's a limit on what you can earn, say 1 trade per min results in extra $$ and XP, that's still free money and doesn't require any skill. So let's rule out direct income.
Extra Access: This option is more plausible because of the similarities it has to the realtor in terms of money making. Both jobs invest in something and have to wait on an outside force to determine when and how much income they may or may not make. Stocks are just a little different because while they don't need another player to buy, there is a random chance to lose quite a bit of money. Not to say that isn't possible with houses, but let's stick to principle ideas. This means that to make the Stock Broker job worth getting, you would have to make it better than just using /stocks. Problem is, /stocks is already completely accessible by anyone. And my guess is not everyone is even using it, only a handful of people are. So to make a Stock Broker relevant, you would have to restrict everyone else's access to /stocks, in some way or another. While this worked for real estate, because just about everyone on the server was getting involved one way or another, it wouldn't work for stocks. Not enough people use them regularly, so restricting access just to force those who do use it to get the job isn't worth the effort put in to integrate the job onto the server via plugins.
tl;dr In my opinion there isn't a good enough mechanical reason to implement a stock broker job. While you could certainly roleplay a stock broker/investment manager and make some money doing it, there isn't a need or a good way to create a server job that fits.
