I think they're assuming that the leavers are people who were concerned and did research about it and decided to leave, while the accepters are "john/jane doe"

I think they're assuming that the leavers are people who were concerned and did research about it and decided to leave, while the accepters are "john/jane doe" sorts of people who dont actively question their use. It doesn't airtight-ly support their claim, but it's sort of plausible to me? Especially if we're separating [facebook for personal use] from [facebook as ad platform for promotion of myself]. I could see influential people deleting their personal accounts and continuing to use their professional accounts / run ads.