For most hackers or wanna-bes (often called Script Kiddies, that is, people (generally young, even children thus the "Kiddies") who are not technologically inclined enough to be real hackers and see a tutorial online on how to run pre-written scripts that repeatedly perform various functions), the answer to "Why do you do it?" is often:

1. "Because I was bored."

2. "Because I can."

Very rarely are other reasons given.

Some people enjoy causing suffering to others. On the internet they are termed trolls. Irl people usually just call them assholes. Most people have encountered them before.

I think they are far more common and likely than anyone giving two shits about reddit.