EFF claims that caching is not a integral part for ISPs. They use Sonic as an example, but why no mention of other ISPs? Doesn't this link say otherwise?
"For unanticipated traffic spikes, Comcast absorbs the excess traffic by automatically spreading traffic to multiple CDN caches in the same metro. Comcast has over 100 separate caching locations in the U.S., and spreads its CDN traffic to multiple proximate physical locations in each major metro without a tradeoff in performance. These CDN locations are strategically deployed across the U.S., which (1) enables delivery in large metro areas and (2) more evenly spreads demand to prevent congestion that commonly impacts high throughput HD video and large file downloads. In addition, the Comcast network is well interconnected with many other networks. This enables high-quality content distribution, and allows content to be localized for distribution just as effectively."
https://www.comcasttechnologysolutions.com/blog/how-comcasts...