It's that some consoles like the (S)NES were extremely popular, sold in the millions. And some games sold in similar numbers. Or were expected to. Or custom IC was (expected to be) used in a # of games. Or some of these publishers were just awash with cash + crazy high expectations for their products. Or some combination of the above.

Iirc for custom ICs, you're usually talking about production runs in the many-thousands. Say, 10k+.

But in the above example: if $60 provides a $10/sale budget, 10k sales gives you a $100k budget to work with. 100k sales -> a cool 1M budget.

Numbers add up quickly if it's mass-produced and 'everyone' buys one.