I can't speak for others, but in my case it is indeed one of the reasons. I am using my iPhone and iPad solely as communication, productivity and entertainment tools. The consistency of experience, the relatively higher app quality and slightly improved ecosystem safety are valuable things to me. I can still create whatever application I want in XCode, as long as it doesn't push the boundaries of the allowed, and yes, those boundaries are a restriction, but one that I am fully aware and accepting of.

I am also fully aware that if I want a mobile hackable device I will have to find another option and I am fine with it.

And by any measure, this already put me in the minority of minorities. I doubt most users would want a more open iphone if they are made aware of the trade ofs. Why should a businessman want to know more technical stuff in order to use his phone? just so we geeks would be able to sideload stuff? Well, he don't want it, he actively don't want the device to give him this freedom, because them he would have to be aware of boundaries that he didn't have to before, more cognitive workload for him for no value added.