Because he doesn’t make profit from his wine as far as we know.
Well, he still can. By exporting them outside Federation. Federation is a non monetary state, yes. But everyone else still conduct trade. Even in Bajor, Deep Space Nine still conduct trade.
There are also several bars / night clubs in Star Trek universe. Quark will definitely welcome Picard's wine. The bar / nightclub in Picard season 1 will definitely accept, and Raffi husband can also become Picard's chateau regular costumer.
Plus, Picard also has Laris, an Ex-Romulan Spy. So even if Picard is ignorant to Monetary sense or trading sense, Laris doesn't. I'm not sure that Romulan is also a non monetary state. They definitely conduct trade. Like Dominion also conduct trade.
With those trade, Picard will definitely need one or two freighter, and if Rios can buy a ship like La Sirena, Picard definitely can buy a better one.
So, in a sense of capitalism, Picard is basically not poor. He's rich. But of course, his richest will depend solely to the writers judgement. If they decide that Picard will only give his wine for charity, then that's it is. But in the universe sense, he has a lot of opportunity to generate profit, and buy a descent ship from outside Federation, like Rios.