- Bragging rights
- Experimentation
Edit: Also potentially political or personal. Eg Posting something that offends 8chan||nation states etc.
There's quite often blackmail involved (Pay us $x BTC and we go away).
Cloudfront or similar should offer DDoS protection for free as a gesture of goodwill, it's good bragging rights for CF so everyone wins.
Well, it is still a lot of wasted resources (bandwidth, energy, compute) for everyone involved (ISP, CF, attacker, defender, compromised machines), so I wouldn't be so quick to say that "everyone wins".
They were talking like twitch chat at times.
Being able to take down such big websites would probably go a long way in giving them some credibility when selling their services.