Good point kevinm,I'm no expert by any means (I'll eat humble pie if necessary) the Audi Q3 for example does light up all the way as you describe but this is a single unit that sweeps under the tailgate.
The golf's tailgate is 2 units on each side.There is a cluster that is on the tailgate itself.The new Audi A4 avant has its rear lights in 2 parts like the golf does.Ive just watched one on YouTube and only the outer 2 light up same as golf.
It might be because the Q3 is a single unit that they can legally do this.
I'm happy to be wrong won't be the first time.