Thing is, consoles don’t need as much ram as a computer because all that ram is dedicated to games. Computers run a lot of applications at the same time and thus need to have more spare ram than consoles.
4gb for a console is a lot in comparison, since the amount of ram the OS needs is very small and the rest is for games only.
To put it in perspective, my PC has 4gb of ram and right now it’s using 2.4gb of ram between all the shit I have open. In a console, let’s reduce that amount to something like 100mb at max just for the OS and all its apps. That’s 3.9gb just for games. Not even the newest, most demanding PC exclusives in the market right now need that much.
Now add to that the amount of optimization you can do in a console game and you can guess how impressive that amount of ram is for a console.
edit: and computers always need some spare ram left to work properly, consoles can just fill it up to the brim and don’t have to worry about unexpected stuff getting on in it.