The dev seems surprised by what is pretty common knowledge:

• You get only roughly 50% of gross revenue paid out after distributor cut (30%), vat (10%) and returns (10%).
• Games make the vast majority of profits in their first month, only ticking back up slightly when releasing DLCs.

So there are only three things to do really:

• be happy the game did well, do 1-3 months of patching, and go on to the next game (and do your best to ignore angry gamers yelling that “the game is abandoned”)
• the paradox route: keep releasing regular DLC to keep cash flow up while also releasing regular free updates (and do your best to ignore angry gamers yelling that you are a greedy evil corporation)
• introduce micro transactions, subscription models or any other way to keep making money after release (and do your best to ignore angry gamers yelling that you are greedy)

Instead, for some reason the dev seemed to think they can keep up developing the game indefinitely and that somehow, it would keep making money? There are like 10 games in history that made enough money to allow development for years: Minecraft, Terraria, Witcher 3, Stardew Valley, etc. And I don’t think they are even cash flow positive on their own.