- Advertising for potential DDoS service buyers
- 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.