Five simple reasons: Apple, Google, Amazon, Facebook, and Microsoft.
Many people use, as a kind of shorthand, The Internet to mean a wide variety of things related to this series of tubes. The Internet could mean the culture made and distributed on the Internet, the LOLCATZ, memes, etc. ("The Internet loves this kind of stuff.") The Internet could mean the infrastructure itself, its speed and distribution. ("The Internet is so sloooow right now.") The Internet could mean the industry that builds it, the consumer and B2B companies that effectively own all the quasi-public spaces through which we traipse. ("The Internet wants to disintermediate blahblahblah.") And there are a thousand other times when we find it easier to say, "The Internet does" or "It feels like the Internet is" or whatever rather than attempt to identify the specific actors of the play.
And maybe that was helpful. Maybe in such a distributed system it makes sense to use "The Internet" as a stand-in for causal agents that seem to inhere in the network without belonging to any individual node. Maybe it's like a mob or a gatheration of starlings; the dynamic relationships between the individuals turn out to be more important than the things themselves.