You're forgetting latency. Speed of light isn't getting any faster. With all the round trips that TCP/IP makes, and the congestion control and TCP slow start (

You're forgetting latency. Speed of light isn't getting any faster. With all the round trips that TCP/IP makes, and the congestion control and TCP slow start (especially if your connection occasionally drops packets, which often happens on mobile / wireless connections), surprisingly little additional data can add a surprisingly long delay. Especially considering the multiple round-trips to third-party servers often required by JS libraries.