I think the nearest car analogy is ODBII ports and data access - ANT+ is a wireless communication protocol, mostly for reading statistics (I think it can also be used for issuing commands).
Hammerhead had a license to access the privately configured Shimano data - and then they were purchased by SRAM (who are Shimano Bike division's main competitor).
As a result, Shimano is (for now) limiting a competitors ability to see the data produced by Shimano components.
This feels very petty to me - most of the data is essentially going to be "which gear is the front/rear in", and "what shifting pattern do you want to use" - though it might also extend to preventing future interoperability (like preventing competing wireless shifting levers triggering the other manufacturers components) - which would be a loss for consumers.