I certainly don’t think all men are lazy. Many men work incredibly hard and are very motivated and proactive. There are tons of lone fathers, through bereavement or relationship breakdown, who work just as hard as lone mothers. Men who care for their partners, parents or other loved ones. Men who are proactive and equal partners.
But I agree in general, straight men have been socially conditioned (as we all have) to sexism, leaving women to be their (unpaid and often unappreciated) domestic servants. In my experience, this can be particularly true of men who had mothers who didn’t work outside the home at all, or much, in their formative years. So, their reference point for women in relationships can be they do everything, or most things, at home and/or with childcare.
They may have also learned from fathers, grandfathers or friends an attitude that men go out to work in physically demanding (especially back in the day), ‘important’ or higher paid jobs, so shouldn’t be expected to devote time or energy on things at home. They may subconsciously view cleaning or childcare as less important jobs, even though they’re essential and valuable. And some just seem less ‘house-proud’ than women and don’t appear to notice mess or grubbiness, even when living without a woman.
But I’m not sure it’s usually due to laziness, as men who don’t share household tasks often have plenty of enthusiasm and energy for things that are important to them, whether it’s their job, sport, socialising or other hobbies.