You're just assuming that they're both lying about the motives, and making up the worst possible motives you can think of for each. I think in both cases you're wrong, and the stated goal is the actual goal. (Apple is not looking to lock down their platform with this, and Google is not thinking about ad blockers at all here.)

Their reasons for needing such an anti-abuse primitive are not the same, but the mechanisms are very similar, and the range of attestations they could provide without public opinion or regulatory backlash is probably almost identical.