> Both of these acquisitions were reviewed by relevant antitrust regulators at the time. The FTC conducted an in-depth “Second Request” of the Instagram transaction in 2012 before voting unanimously to clear it. The European Commission reviewed the WhatsApp transaction in 2014 and found no risk of harm to competition in any potential market.

Just because they were reviewed to be legal at the time does not mean they're legal now, also it does not mean they were right back then. I believe the FTC isn't subject to the rules against double jeopardy like the legal system.