[ElmntOfSurprise]

If Apple user visits contribute less to the earnings of a certain class of websites (news sites, for example), then these could lose interest in the visitors and not optimize content for them. This could e.g. lead to websites breaking when visited by Safari.

I believe similar reasons led Firefox to formerly only offer their tracking protection feature in privacy browsing mode. Possibly their analytics showed that it turns out that most people don't activate that feature, so they now offer it in all modes. Privacy-conscious FF users in a way free-ride on the masses who use FF without knowing / caring about the feature.

It will probably go similar for Apple: They make the feature opt-in, most people don't care and leave it off, nobody gets hurt.