Why? Intel invented it.
But this is a really good thing.
Actually it's more like "co-invent", Apple requested for a technology like this and offered the original direction, then Intel's engineers and Apple's engineers spent some together and realized it. That's why Intel allowed Apple to announce it before itself did, and allowed Apple to have exclusive access to the technology in the first year. Of course, when we look it back, that "exclusive access" means nothing to Apple, as the eventual ThunderBolt uses a totally different connector from the earlier versions.