There are many reasons and I'm not a weeb either per definition though I do often call myself one.
Originally, weeb meant denouncing your own culture and only embracing japanese stuff but it's gotten to a point where you just jokingly say you're a weeb if you like japanese stuff *in any degree*
"Weebness" in its worst form however, would include things like giving up on finding your own identity and any relational happiness in the real world and using non-real characters as a proxy. So it's a big spectrum.
