I'd say the reason why men don't flirt is that there is nothing left to flirt with. By and large women are trained to keep their heads glued to the phone, never make eye contact, don't do anything that might give a man a glimmer of hope that their flirting might be received. I have serious doubts whether most women just generally don't like most men and women love that men don't flirt anymore. I wrote my own article about this asking if women have completely given up on men.

https://franklinwuhoo.medium.com/have-women-completely-given-up-on-men-8ead16dae877

Unfortunately, I think so.