[Non-SEO]

Here is one explanation about that why the love-havers (and/or s@x-havers) don't understand the incels: privilege and social mobility.

[MSL]

I will say it here again, simpler  -- those who have tend to think more that the world is just and everyone has what he/she deserves.
Sometimes it's true -- for example some NEET incel (NEET = "Not in Education, Employment, or Training") who is lazy, obese, wih a low IQ and so on really doesn't deserve another person (a girlfriend) because he is not a "good quality" person (able to provide, protect and so on) + he's not putting efforts in his self-development. From any point of view he's not deserving to be in a relationship and the potential girlfriend is not deserving to suffer with this kind of incel.