I agree with your concerns and have also mentioned a couple of time, for example in the day 7 update I wrote "Now I am curious how they generate revenue, probably by advertising or subscribing. I you know, let me know.".
Since then, there seems to be 3 ways that they generate revenue. Firstly, by having people deposit BTC to accelerate progress. Just like we see in many games, even the popular Helldivers II.
The second way, is by advertising other channels and events. Marketing in essence.
The third one is still new. Telegram just announced that channel owners will be receiving a payment, depending on the number of interactions the channel has. A split of revenue. Still new, but this could drive a lot more games and channels trying to get attention.