Where exactly does the quoted text mention shady spam operations? It's about DDoS victims, not cybercriminals.

>We are NOT a DDoS Mitigation Service. Yes, we have a lot of DDoS mitigation in place. No, this isn’t here so that you can get cheap DDoS mitigation. You cannot use any services here if you are, have been or think you may be the direct target of a DDoS attack. Contact us instead for a referral to a real DDoS mitigation company. If you come on this system knowingly bringing a DDoS on your heels we shut down service (we may also wildcard your DNS to localhost and set the TTL on your zone out to a year. You’ve been warned).

> If you come on this system knowingly bringing a DDoS on your heels

So hosting a minecraft server? Or a game server of any kind? An IRC server? An internet forum? An email provider?

All things notorious for attracting DDoS attacks.

What motivates a DDoS attacker? Are they all just wannabe vigilantes seeking to right some perceived wrong (such as being banned from a club, opposing political views, etc)? Is there ever a clear economic motive?

Yes, most are wannabe vigilantes.

Sometimes ransom but CloudFlare has kind of killed that line of business.