Winton never charged 20% Mgt fees. You probably referred to performance participation?
Trend following did very well in the decades upto 2010. But since then has been quite poor. David Harding/Winton one of biggest trend followers does not feel justified to charge clients 20% fees anymore and is only charging 1% management fees on his trend following fund going forward.
Seems there are too many large funds doing trend following and the space has become over crowded and this has weakened the edge.
(btw, PTJ and Cohen were never managing trend following CTA type funds, but i know what you mean, many other managers did get rich from running trend following funds in the past.)