Permanent beds for each veg?

Next daft question

I don't know about you, obviously, but I have never followed any of the soil rotation plans  - where a specific group of veg move to another area each year - the theory being that each veg benefits from whatever was grown there in the previous year. Don't expect me to explain it  as its beyond me!
I've realised that I always grow beans in the same place - always grow peas in their own place, every year - because that's where the supports are.
Perennial vegetables - leeks, kale etc stay put and seem to thrive. ...............
.........So, why, are we advised to grow annual leeks and brassicas in a different place every year?

You can probably see where I'm going with this........to create permanent "beds" for each veg that I grow. It would have the added benefit that self seeders would be in the right place to grow, year on year.