Of the purchase price that the end-user pays, the retailer has to pay tax. That knocks off a variable percentage. It would be 20% in the UK.

There's also the cost of selling through Steam / Google Play / Whatever - typically 30%.

I assume the developer has some professional expenses - an accountant at a minimum, probably a lawyer, certainly insurance. Maybe they also have a PR team, advertising, and the like. I don't know whether they pay for testers, translators, and things like that.

Then we get on to things like buying a new development machine, going to tech conferences, taking an educational course, backups, and all the other things that a business needs to spend on in order to be effective.

Maybe a profit margin of 10% is unrealistically low - but developing software has legitimate costs. The margin is never going to be 100%.

What do you think the profit margin of canned goods is? They make cents on every can. Something like 2-3%.

The video games industry is filled to the brim with gatekeepers who take their cuts. Valve takes 30%, just for their store. Publishers start at 10%. Your engine might take a cut.

Estimating that Stardew Valley, the big success video game with the lowest overhead bar none, has made 10% profit might be too low. 20%? Might be high.

Besides tax and the store's cut, the games also regularly sales and prices-changes. So you can't just extrapolate the price today with the amount of units sold and assume this to be the revenue.