- Relay attacks can theoretically be solved with high precision clocks, but will affect price and reliability in a negative way
This obviously depends a bit on the situation, but most relay attacks happen within reasonable proximity. Most attacks happen to a car parked in front of a house, since the attacker knows that the keyfob is likely to be within the house. The distance here is often less than 20m. To get reasonably reliable relay detection on these kinds of distances, you'll need very precise clocks, which will make the keyfobs expensive and still increases the risk of false positives on relay detection.
What's the point (to the customer) if the expensive ULTRA SECURE (tm) keyless entry system is 10x the price, and still less reliable than the keyless entry system om their 20 year old Toyota?