It’s as simple as that. Professionals are paid; amateurs do it out of love. So, whom should we respect more?
Why is the paid person respected? Because the payment represents an element of control. The amateur exercises autonomy.
On some level, the Dude recognized that. Which is why he insisted he was going to reject the Presidential pay. Of course, that’s not how the system works. We pay public servants exactly because we, the people, expect to be obeyed and exercise control.