My dogs have offleash walks every day. Maybe they are much shorter than yours (probably) but they typically want more, particularly mental challenge, or maybe I have just conditioned them to want it, who knows.Sometimes, but I know of lots of people that only use specific walking circuits and never change, a lot of people mix in a LOT of obedience, many don't participate and explore with the dog and a lot of people simply don't let the dog follow his instincts and just be a dog when safety permits.
I do get bored easily and so I change things up. I don't like to walk the same route every day. We have 2 loops through the woods on my property, and a 2 mile road walk which includes a decent offleash stretch. Sometimes I drive to down and leash walk them which they seem to find very interesting. I definitely think it makes a difference to them to see and smell and explore new things.
And I totally agree t hat dogs need to run free and be dogs, they are so happy and it makes me so happy to watch them. And bonus they are very mellow indoors which is how I like them.