Because privacy is an obvious goal that Apple can crediblebly target because of the nature of what they sell. Google is fundamentally an advertising agency, Amazon sells cheap stuff but steals your data in the process. Apple sells premium hardware and services, which means they have the margin to do things that neither google or amazon has. They also make money the old fashioned way: when you pay them.

Therefore Apple could focus on privacy in a credible manor, because it didn't threaten their business model and it was an argument they could use, but their competition couldn't.