I've seen no evidence or mentions of that particular rationale. They claimed they un-aggregated to support their "pay up front" model and start charging pledges on the anniversary of the pledge date.
They mention it below the original announcement, though they don't give any numbers.
> Not only that, but if you’re a creator on the monthly plan without the benefit of charge up front, you are constantly worried that your patrons are going to delete their pledges before they’ve paid.
That doesn't say it was requested by credit card processors. As I understand it, the concern there is that they don't want people to pledge, get access to patron-only content, and then revoke their pledge.
