There are two reasons why the signs on the highway are so prominent:
1. When you are driving a car, you are basically meat bags inside 1.5+ ton collapsible metal cages moving around at 30+ or even 100+ km/h. One wrong move and meat bags risk being injured or killed. That's why the signs need to be simple and prominent.
2. A highway network has one and only one purpose: to transport people and things around, so the number of things that you can do on a highway network is inherently rather limited, which is why you can make decisions fast: go faster, go slower, stop, yield, merge, change lanes, exit a ramp, enter a ramp, turn left, turn right. That's why the signs can be simple and prominent.
Neither condition applies to websites in general:
1. If you lose your way on a website, you generally won't injure or kill anybody.
2. Websites generally don't have one and only one purpose, the number of things that you can do on a website cannot be expected to be limited. You could argue that the website menu should have one and only one purpose - to bring visitors to various pages - but that's not always true either.