We don't know what went on with Clijsters... Sometimes a coach pushes you in way that you (almost) hate in order to achieve a goal, so much so that you just don't want to do that anymore (or you need a mental break from all the stress & pressure of the past weeks, and your coach was at the center of that and falls victim to it). Maybe you don't want him to push further in that direction, maybe you think you can achieve the same with what you learned and without the things you disliked in the preparation... or maybe the coach said things afterwards - to you or others - which bothered you (like taking more credit than you feel he deserves, asking more money, or proposing further changes you don't want to).This. And even the perceived 'nice' players do it - didn't Clijsters dump hers straight after her first US Open win when she also won the US Open series and had a MASSIVE pay cheque?
Again, I don't know what went on to further defend Kim (even if I indeed consider her one of the nicest players out there). In Halep's case though I feel it's more the obsession with Darren than anything else, which yes, makes her indirectly & involuntarily "not nice". Cahill helped her. A lot (in a way). But even so, she still gives him a disproportionate amount of credit for her accomplishments, because she doesn't want to acknowledge his shortcomings or bad decisions about her development... while when it comes to Dobre (or Pavel before, perhaps Fissette as well) she underappreciated their contribution.
Anyway... no point dragging her because of it. She's paying the price herself. Without the Darren obsession she would have had more slams (& money) by now, with a few more in the future as well perhaps. Now, I just don't see it happening anymore, because instead of maturing and becoming more independent, she just grows more and more dependent of Darren. Luckily he's not as bad for her as Sumyk was for Garbi. But unluckily he's too far from being a complete coach that could help her maximize her potential.