I get your point, but this feels like an odd place to make it. The idea that all application developers could examine, record, analyse, and eventually abuse something as personal as your gaze tracking data is truly terrifying, and the fact that Apple doesn't allow it is something that makes me feel more comfortable buying a headset of theirs that has the feature in the first place.
Well, if I don't trust them at all with it, then I simply wouldn't buy the headset (it's inoperable without it).
But at the moment, one of the biggest selling points for Apple is privacy and the responsible handling of your data, so out of most other similar organisations I believe they have an immense financial incentive to safeguard the data. And I think their actions so far speak to this being a critical strategy to the success of their business.
Regardless, whether or not I trust Apple with it, it's certainly a lot easier to trust just Apple, rather than Apple plus hundreds/thousands/hundreds of thousands of others whose incentives are much less clearly aligned.
