I'm not defending HOD but my take on this is that many girls, mostly non-Brit, prefer a parlour since they don't have the problem with finding their own accommodation and advertising, plus it's far safer for them. OK, they have to hand over a certain percentage of takings to HOD, but this could still be more than they would earn as an indie, taking accommodation expenses into account.
Getting rid of unreliable employees is not just known to this industry.
I'm very happy with using HOD and have never had any serious issues with them spanning over 7 years!