A: Cloudflare is feeding the trolls because they think that they are invincible. Or: These post-mortems don't establish any proof that the attack was successful, especially if they are covering DDoSes that were barely even noticed by the public until CF publishes a blog post 1 month later -- so it's actually embarrassing for them and hurts their ability to market botnets for rent, at least once they no longer have the literal world record.

B: Cloudflare is feeding the trolls for free testing scenarios to improve the mitigation

C: The trolls don't really care if you feed them, large DDoS is something that's happening all the time anyways

Isn't the obvious point that this is Cloudflare advertising their anti-DDoS services?

Also it makes no sense - why throw 7.3tbps at a server, when half of that or less would have the same effect and not exposed your botnet.