PvP is a thing but just existing doesn't mean that you can't possibly protect something, or have incentives to keep it around that are strong enough that not everyone wants to destroy it.
Aside from the stock thing, which you can do in various different ways already (and this is not MLM, a pyramid scheme has one person on top who makes more money the more people there are under them feeding them money. What I was suggesting was a flat field where people make a percentage of the overall profit of the station based on what percentage they contributed and is more along the lines of earning dividends on a stock), just straight up issuing and buying stock for the station being the most straightforward... okay, a few different ways. I'm not saying that they are guaranteed to work, just that they are ways that you can try to keep the station alive. In no particular order
1) Just build a really big faction to protect it.
2) Build a coalition, possibly by handing out free slots in the station to people who assist in the defense, or giving tax incentives to lure people in to occupy the station so that there are more parties coming in with a vested interest in keeping the station around.
3) Have an amazing location that promises becoming an important hub of community interaction, as a refueling port or place where players come regularly to socialize.
4) Pay tribute to scary entities so they don't feel like attacking you
5) Become a semi-autonomous entity under the control of the strongest group around, pay them most of your profits, and be willing to do the same to anyone who conquers those guys
6) Like I said before, if possible build within the safe zone of a starting station.
7) Have an amazingly bad location that nobody actually wants to go to for any reason other than trading, with no meaningful minerals resources nearby to make it less worth people's time to attack
8) Make your station using a starting station as the basis of it,and just rent out your slots to others, guaranteeing that it's a completely safe zone
And so on. The initial question though was how to make the station profitable enough to justify protecting it. That shouldn't be hard because the thing is basically supposed to be pointlessly massive, which means lots of vendors, lots of money changing hands, lots of rent and lots of opportunities to tax people. You can try to make it a status symbol to own a residence on the station, offering large luxurious "homes" or places of entertainment, like a race track or an arena. If people value the existence of the station and have a vested interest in it existing, then they will want to protect it. I think the harder part is just finishing building the station in the first place, which is why I went with the idea of investors. I feel that's the most feasible way that you manage the initial build, if you don't have a massive faction backing you in the first place.