I've seen a lot SEO motivated DDoS attacks in very high value money-keyword niches. An attack basically downs a site for an extended period of time. GoogleBot notices the slow speed and logs dozens of 500 errors, which can result in dropped rankings.

I did a quick check for usefathom.com though, the only somewhat interesting keyword would be "google analytics alternative", but fathom ranks on page 2, which imo would not really justify an attack. Maybe there is some other long-tail keyword with a high enough value though where usefathom.com pushed small niche players out of the top positions.

Also a DDoS is obviously bad for the user experience of paying customers, nobody wants their analytics service to be down or have missing data bc of downtime etc.

Perhaps AWS needs to sell AWS Shield Advanced? Ha ha, I'm probably too paranoid.

And why? What is "Fathom", what do they do that could have triggered such an attack? Or was that an attack to deliberately force them to turn to Cloudflare for "help"?

Some proxy engaged by the competition?