This could be part of it. The shift to mobile computers which are necessarily wireless which means a random round trip time due to physics, which means TCP back-off. That, combined with the tendency to require innumberable external JS/CDN/etc resources that require setting up new TCP connections work together to make mobile computers extra slow at loading webpages.

Bandwidth and latency aren't the same thing! High-latency networks sometimes don't ever load some websites, even if there is reasonable bandwidth. I remember one time when I was in Greenland having to VNC to a computer in the US to do something on some internal HR website that just wouldn't load with the satellite latency.