The system works like this:
Apple sells a mostly closed hardware product to clientele with a high vanity quotient?, and wallets to match.In this model you don't incremental upgrade your machine, you buy a whole new one.
However, real work must be done - expansion and connectivity is needed. How do you reconcile that need with a closed box system?
You build high speed external I/O, and and you do it on the bleeding edge - and you can afford to do this, because your clients will pony up.
On Windows, Thunderbolt is mostly
meh. Nice to have, but there just isn't that many use cases to justify it at the current moment. USB nicely fills the bill and is more than capable of providing enough channels to choke today's CPU. So the thinking is, let the bleeding Apple folk amortize the cost of developing/debugging Thunderbolt and us regular PC folks will sit tight tol then.
Microsoft finally took notice with of Thunderbolt with the introduction of USB-Type C, with its alternate mode transmission. It's future proof to a point, and by allowing other protocols, it doesn't box them in with a technology controlled by others. I'm guessing it'll be another year before USB-Type C/Thunderbolt etc make it to non-gamer PC's.