Volonteers are doing a lot of work, sure. But how much value exactly is this work adding to BGA ? Hard to say with precision.
All the popular games are now always done by freelance devs so if volonteer dev is working on something, it's more likely to be a niche game, and thus won't attract a lot of new players, which is the main source of revenue for BGA (actually, only the premium would mater).
What I am trying to say is that probably BGA could nowadays run without any volonteers, maybe with less new titles each year, maybe with some extra cost if hiring translator, but that would probably still be something financially doable.
Obviously that's not the mentality of BGA and I love that the site is gathering us as a community, but keep in mind that BGA also brings great value for the volonteers : it offers a framework that allows to "easily" add new games, while handling all the licensing part, the lobby, the servers, the exposure of the players pool of the whole website, rewarding with premium membership and sometimes IRL boardgames gift.
To sum things up, I wouldn't state that BGA is making money out of volonteers' work, it's more nuanced than that.
To go back to the original topic, I would agree that from the player's perspective, it's not obvious at all that BGA and game developpers are not the same thing and it would be great that more information were displayed about that on a game page. (was it done by a freelance or volonteer ? is it still actively maintained ? ...)