The existence of other ARM SoCs doesn't mean they're competitive enough at the high end for the advantage of open source drivers to be the determining factor.
Meanwhile the low end is more sensitive to price than quality, so competition there pushes things towards things cut costs rather than things that improve the experience, or even things that reduce long term costs at the expense of short term costs.
Meanwhile the low end is more sensitive to price than quality, so competition there pushes things towards things cut costs rather than things that improve the experience, or even things that reduce long term costs at the expense of short term costs.