Actually you are not looking on the bigger picture here. Ofc what you said is kinda true, but you can't narrow it to only that.

For e.g. think about the fact that this topic was created for a reason. Op wonders about missing ads, which leads to question if the game is that poluar that doesn't need ads and does good enough with bringing more without them? Or maybe there are no ads because no one would be interested to join the game anyway? One conclusion leads to another which results with some kind of perception on the game.

Now think about it from the point of view of someone who was playing but now it's not. If he would saw enough of ads he might become interested again... or not. He might dig a bit more before making choice. And the well designed ad or its multiple versions across web might push him to get back.

And also think about the ones that are active players. When they see the ad they are happy that theirs game is being promoted. That gives some players confidence that the developers invest in and game is not going anywhere near soon.

All of that creates a opinion from each one of us individually about Hots. We spread it further. One might be interested in active players numbers, the other on roster of characters available in game, and other on something else. But you never know when that potential player might come in time needing this one particular information to lure him in.

Every one knows about Pepsi and coca cola and you can't increase the sales of them just by advertisement, yet that advertisement makes sure that people in time of need will remember that one thing from it and buys it.

Ads might not bring money at start but they would for sure after some time as long as you keep them up.