Well, it's connected to both of those reasons.

For all of humanity, you have to love SOMETHING. Whether it's the most social butterfly in the world or the biggest ace person in the world, you have to have some thing that you feel love for to make your world a little brighter. If you can't get that date, get a pet. Can't have a pet, keep a houseplant. Can't even keep a houseplant, throw yourself into work, religion, hobbies...and yes, you can't even do any hobbies, throw yourself into a fandom- and waifuism is just an example of throwing yourself headfirst into a fandom. It's kind of questionable, but even if someone's so depressed all they can do is find a character on a TV show they'll never meet- meaning they can't accept or reject them- through it...sure, whatever.