What is a lot of traffic to you?
2.5 million downloads of 4 GB are 10 PB of traffic.
I think there are be a lot more than 2.5 million Chrome users in the world.
You only download it when some JS requests it for the first time, most people will never have it.
Wikipedia say 3.6 billion Chrome users.
More data moves in your average playstation system update than that. Steam probably transmits more in a morning than that