Actually, it's photography, so we probably don't have to buy the features we absolutely need. If someone wants to just play around with some feature, why not buy the camera that has it? We don't have to *need* something to buy it, otherwise some of us probably have to sell 90% of our lenses
Is eye tracking a pro feature? It might be, but so is face tracking. The two are probably interchangeable in some professional situations (sports, weddings). I can't think of an application where eye tracking works and face tracking doesn't, except for "one-eye-in-focus, really-shallow-DOF porrtaits", which of course is an amateur type scneario, but one that a lot of people pursue because I guess it can be fun.