Why do video game consoles such as the PS, Xbox and Nintendo have better graphics and performance as compared to a PC?
Short answer, they don't necessarily
Longer answer:
A console has the advantage of being single purposed. The aspects of its design can be optimized for gaming at the expense of all those other things that a regular computer can do. As a result, it is tough to find a computer for $250 (Approximate price of a basic Xbox One these days) that outperforms an Xbox One, at least in regards to the console's speciality.
At the same time, most people don't buy computers with a good deal of power behind them, and are often buying them from companies like HP and Dell, which have poor reputations among computer savvy customers for a reason.
However, if you buy the right model, or better yet learn enough to build a tower yourself, achieving performance and graphics in a PC that blow consoles away is a very simple achievement.
My current desktop houses a CPU that is almost twice as powerful as the one inside the brand new Xbox One X (At least on paper, I haven't seen performance tests for the actuality), I've had it for the past four years, and I didn't have to break the bank to purchase the parts for it.
Edited: daishain on 21st Jan, 2018 - 5:35am
What Daishain said is correct, its cheaper to buy a console than a PC that can do the same thing but I want to add a couple of other things too. Most people just want to turn on and play they do not want to be fiddling with a video card trying to find optimal settings like they would have to on a PC. Since you can hook up to your big screen you don't have to be limited to PC monitor size and last people want the controllers rather than a keyboard or mouse interface.