Its much harder to analyse web request that don't generate a cascade of derived requests. The signature of a page visit that pulls in a bunch of different sized

Its much harder to analyse web request that don't generate a cascade of derived requests. The signature of a page visit that pulls in a bunch of different sized resources from a plethora of advertising sites is much more distinctive. If the great firewall wants to know what you are reading, or if that TLS connection is actually a tunnel, the request signature is very useful. Even for sites with a CSP requiring everything encrypted this is still useful. It is quite feasible for state security to place ads for content that matches China related content. Even internally in China, having websites load ads is very useful for tracking and injection. Local ad serving companies will cooperate completely with the provincial and national security bureau. See also, Great Cannon: https://citizenlab.org/2015/04/chinas-great-cannon/ https://citizenlab.org/2015/04/chinas-great-cannon/