It may be royalty free but getting access to the chips and reference designs still requires signing an NDA with Intel (which they may or may not even give you a chance to do). They are still the gatekeepers for the technology because no one else makes comparable chips.
Apple can’t until either: Intel opensources thunderbolt or Apple drops Thunderbolt support.
Years ago Intel said they would but they still haven’t yet.
Edit: I originally stated Lightning and meant to say Thunderbolt.