Because Apple doing this transition in a much better way. First they introduce some better system (for ex: content blockers), waiting for it to be successful from user perspective, then replacing old system with this new accepted one.
How is that different from what chrome is doing? There's a deprecation plan, it doesn't appear to be significantly shorter in time scale than what apple did.
Advantages: privacy, efficiency
Disadvantages: lack of flexibility, some things they just can't do
I only ever read that hypothetically it could be more efficient but never stumbled upon actual measurements/benchmarks.
Also, extension adblockers are already so efficient that I would doubt there is a perceptible difference.