To be fair, they probably are investing the money, in case of a rainy day. Such as if they were to royally piss off their current Patreons, and suddenly find themselves only earning 40k a month, and yet still have to keep paying staff.
Also more staff doesn't mean higher productivity. More staff means you need more coordination, communication, and uniform development standards. For example: Take Elder Scrolls: Morrowind, a game that most feel is one of the best games in existence. Then take Fallout 76, deadpanned as a piece of shit. Same developer, but when they made Fallout 76, they had roughly 4x the staff as they did with Morrowind.
So, the lesson is, grow the team at a rate that is beneficial for the development team.