As already mentioned by others, AMD won the console market because back then the only thing they could compete on was price.

Which coincidentally, the most important thing to Sony and Microsoft with regards to consoles ("make tons and sell tons" products) is cost of materials. Even getting that cost 1 cent cheaper still means a $1 difference over 100 units, $10 over 1,000 units, $100 over 10,000 units, and onwards. Remember, we're talking many millions of basically identical units sold.

AMD couldn't compete in performance nor efficiency, but they could absolutely compete in price, while both Intel and Nvidia couldn't due either to their business strategy or the logistics for Sony/Microsoft of procuring more materials from different suppliers.

So long as AMD can continue to undercut Intel, Nvidia, and any other contenders they will continue to dominate consoles.