Why do some cheek implants look like balls in the faces of the patients?

It is difficult to say whether a person has had Plastic Surgery from a photo and also to determine what kind if they have had it.  Cheek fillers, fat injections and implants are all used to make a cheek appear more full.  Any one of these treatments can contribute to a 'overly' done look.  I find fat transfers to be the most natural appearing since they are your own tissue and can be added in stages to the effect you want.  

Hello and thank you for your question. There are many options to enhance and rejuvenate the cheeks in a natural appearing manner.  If malar implants, fillers, or a SMAS facelift is performed with good technique, this can achieve a natural look.  Make sure you specifically look
at before and after pictures of real patients who have had this surgery
performed by your surgeon and evaluate their results.   The most important aspect is to find a
surgeon you are comfortable with. I recommend that you seek consultation with a
qualified board-certified plastic surgeon who can evaluate you in person.
Best wishes and good luck.
Richard G. Reish, M.D.
Harvard-trained plastic surgeon

It could depend on a number of factors, but mainly the timing of their procedure. Cheek augmentation can be done with fat or implants, but also with fillers, such as Radiesse, Voluma, and Sculptra treatments for collagen building.  Please see a professional for an evaluation.  Best, Dr. Emer