Because development/estate covenants require it!
We are exactly the same as you - I want a productive & edible backyard - but as the back yard is visible from the golf course - it must be done in a fashion that appears "landscaped".
I think I read something by Jamie Durie who said that you should spend between 5-7% of your land value on landscaping - and at that amount you would not be overcapitalising.