As far as I know, cPanel is not free for any other VPS provider.. They add the charge hence doesn't show separately..
Yes, it is true, when buying bulk cPanel is bit cheaper but not less than USD 15 a month for per VPS.. So if you may check, those who doesn't charge separately for cPanel is considerably higher in price for same plan compare to without any panel hosting.
cPanel also has a major draw back.. The system requirement.. 2GB is minimum along with a large HDD space..
Here in DO, without these extra requirements, I can run 4 websites in one 512MB VPS without any issue.. Mind you as per many shared hosting with cPanel and unlimited plans refused to host each of them in single account citing load issue..
DO is faster and cheaper.. Much flexible as allows you to pay and install cPanel, if you can afford or actually need that..
I agree with you.. None of the free panels are as useful compare to cPanel or DirectAdmin.. What DO and other VPS (un managed) has to do is fund and help many of these open source projects to develop these free control panel with more resource and better staff to give cPanel and DA, run for their money..