I would wager a years salary if you went around to 100 random iPhone owners and asked them "did you buy the iPhone because it's a walled garden where you can't sideload" 90+ of the responses would be something along the lines of "what is sideloading".

For those that answer "yes, actually" the option for them to be able to use the walled garden would still be there - allowing others the option does not take that away from those that are actually choosing the walled garden vs being required to use it after getting the phone for other reasons.