IMO, Instagram did decentralize, but on a higher level of abstraction. Previously to Instagram, photographers who would want to have their photography seen would have to approach giant centralized agencies for distribution. Now, distribution is delegated to Instagram content creators themselves (but enabled, still, by a centralized platform).
In decentralized systems we see today, both creation and distribution are enabled by full decentralization.
RE: Disruptive technologies, speculative capital, and Thinking Big about Steemit