Part of that control they're seeking includes ensuring a positive user experience. Chrome and Firefox don't really prioritize efficiency anyway, but they're pa

Part of that control they're seeking includes ensuring a positive user experience. Chrome and Firefox don't really prioritize efficiency anyway, but they're particularly bad in that category under macOS, and that would transfer to iOS versions as well. That's a problem for Apple, because users aren't going to attribute their phone getting hot and draining batteries quickly to their choice of browser, they're going to attribute it to the phone. If Apple were to allow third-party web engines, they'd likely have to institute an approval process that includes rigorous testing of energy usage, resource consumption, etc and reject engines that don't meet the bar.