Mostly it's because large numbers of developers have abandoned any pretense of engineering for mobile with their dozens of pull-ins - the same happened when 2g took over from GPRS, when 3g took over from 2g, even in the multiple iterations of 4g.
It's even more painfully apparent out here in the sticks where mobile signal is shit - when openreach fucked up our broadband last year, Netflix streaming was better than simple web browsing.