tbf, they said this is their first adult visual novel, so I would assume it takes a long time. also its likely its only them working on it, and it probably isnt their full time job, just a hobby
Viewing post in Cosy Cafe 0.14 Now in Early Access on Patreon comments
But... It's not good to count other people's money, but according to his Patrion account, he earned at least 14,000 euros this month. In my country, that's equivalent to 10 average salaries. With that kind of income, he could devote himself entirely to game development and hire one or two people to help.
Although, maybe I'm wrong...