Why would someone conduct a DDoS attack on my website?

This morning I was trying to upload a post to LifeTwo but couldn’t access the site and knew it was not just our servers but something that was affecting many other sites at the hosting facility. This message was then posted in support section of our host:

This afternoon [our] engineers successfully mitigated a fairly sophisticated network attack aimed at several of our services. This distributed denial of service (DDoS) attack appears to have originated from China and other sources along the western Pacific rim.

We have upgraded our load balancing system and made various other network configuration changes to prevent disruptions like this in the future. We sincerely apologize for any inconvenience this may have caused and thank you for your patience.

So now I know the reason but not the motivation for why people do this. You read about DDoS attacks all of the time but it is a different feeling when one hits your own servers.