Apple spent years incrementally improving efficiency and performance of their chips for phones. Intel and AMD were more desktop based so power efficiency wasnt the goal. When Apple's chips got so good they could transition into laptops, x86 wasn't in the same ballpark.
Also the iPhone is the most lucrative product of all time (I think) and Apple poured a tonne of that money into R&D and taking the top engineers from Intel, AMD, and ARM, building one of the best silicon teams.