There's also one more issue that I forgot to add...and that issue is actually on legal terms.
You see, the original owner of Feral Heart disappeared, they still technically own it, so if anything were done to monetize the game, well it's technically stealing said money from the one who created the game, models, etc. Or at the very least, would be very sketchy if they decided that suddenly with the money, they want it for themselves.
The problem with using money for a game is it becomes more of a business, and businesses have to have special upkeep, can be sued, and if something goes wrong involving money, they may be obligated to pay back quite a large sum. Since this is all free and wasn't started with a loan, there's an issue with the game being forcibly shut down. Especially if the game were hacked again, and then it's "Bye Bye Feral Heart".
Also, without the source code, we lack the ability to do proper command prompts and even create more servers. So many people spend so much time within the grounds that it already lags really bad, and with the game not always working and crashing, Feral Heart could face one heck of a lawsuit by people who are impatient with the game or feel cheated out of their money for not being able to get into it correctly. Servers get overloaded and boom, the game goes down for however long until it can be fixed, losing more people because they now have to pay for the game. And even issues with the advertisers.
And then there's an even bigger business aspect....actually getting people to WANT to advertise on Feral Heart. Costs money to advertise, why, with how little players there currently are and the game could support, would people want to advertise on it? This has to do with outside advertisers, not for the game itself. But ads for the game itself would also cause too much of a rush and the server would crash anyway.
You do have some points, I would love to have more players but Feral Heart really can only sustain so many. And back onto the paying problem...competitors. There are so many games out there like Feral Heart that offer more, that are free, such as Cereal Soup, Dragon's Den, Last Moon, etc. Which means that logically, unless on an emotional level, no one would want to pay for it because there are games similar to Feral Heart that actually offer more and are more well known, for free.
Now this isn't really a critique, nor is it an attack, I'm just stating the facts of how Feral Heart is, so I hope you don't get offended or feel as if I'm attacking you.