In a nutshell, Yes. You can't park a relatively unknown domain and expect to earn from it. If the parked domain in old and well known, the previous visitors to the site could earn you money, if they clicked on the ads. The beauty of domain parking is when you have lots of traffic coming to the site.So, earning from parked domains is just like earning from the ads on your websites. You need traffic to your domain and the visitors need to click on your ads for you to earn.