That's not true. I work for a company that sells DDoS mitigation products to large network operators like Cogent for helping them deal with exactly these kinds of attacks in a much more sane manner than, "oy, just blackhole the destination and head out to lunch."
Either Cogent didn't buy our product (or a competitor's equivalent), or they have a network op who's a fresher and only knows how to blackhole things. Either way, it's a bad look for Cogent.
I remember at one point back in 2009 or so I wasn’t able to download from one of SourceForge’s mirrors. Turned out the reason for that was that Cogent had cut off my ISP (Telia) for some weird reason. IIRC Cogent and Telia hadn’t agreed on a peering policy, so Cogent just said whatever, we’ll cut you off (:
Either Cogent didn't buy our product (or a competitor's equivalent), or they have a network op who's a fresher and only knows how to blackhole things. Either way, it's a bad look for Cogent.