The disappointment I have when being put in the “friendzone” is that I no longer get to hang out with someone I like. My girlfriend would not be keen on me hanging out with a woman I am clearly attracted to, and it would be unfair to her for me to do so.
If I’m not in a relationship, hanging out with someone I am attracted to, where there is no chance of a romantic relationship, may hinder my search for a romantic partner. Better to just move on with no hard feelings.
If I am not romantically attracted to a woman, then being friends with her is ok.