Because nearly all men think that behaviour is part of being a man. The veneer of civilisation is very thin with most men. It's all part of how they compartmentalise life and don't connect to their feelings.
Depressing though it is I agree with this.
I've often asked myself the question whether a man can truly be a feminist and the answer is unequivocally no. Because they are all socialised in the patriarchy and none of them actually understand what its like to be a woman operating in patriarchy.
Yes plenty of them have been brought up by strong women and civilised man and have learned to curb those elements of their behaviour and that blatantly chauvinistic behaviour is frowned upon. I don't know a single man who would catcall women, I would certainly hope none would harass women or make them feel uncomfortable. And my boyfriend and all my male friends know sexist language is unacceptable in front of me.
But most of this is learned behaviour which they have acquired as a soft skill. For a significant number of them it is something they use to "pass" as opposed to something they believe deep down. Deep down I think the vast majority of them are capable of being creeps, they just choose not to because they are smart enough to understand that that sort of behaviour limits your life chances.
And of course some of them have turned being a "sophisticated" creep into an art form (the yoga teacher who leaves his wife for a younger trainee and claims to have found a spiritual connection with her, the middle-aged executive who goes out a lot with the women in the admin pool but treats them as 'one of the lads'). They're pretty much all capable of it. Some of them have just learned very plausible ways to cover it up.
The only thing I think which has the potential to really change them deep down is having daughters. My ex, who was a proper unreconstruced chauvinist, has radically modified his approach to the idea of female enpowerment since having a daughter.
It's always to some extent about self-interest with men. The only way you can really change it is to get across that there are negative consequences for them in behaving like a creep.