I believe this statement has a lot of truth in it (why else would it exist?!).
I have 5 brothers and 5 sisters. Although the men are in contact, it’s irregular and sometimes don’t see my mother for months. The wife’s family takes first place in every case. The mother of the son is an afterthought.
The same is true for my husband’s family. My MIL had two boys. Both in contact, but she is not a priority to either of them. She is usually first to make contact. Maybe see her every 2 weeks? I see my mother three times a week or so. I don’t interfere with my DH’s relationship with his mother at all - it’s down to him to see/speak to her; it’s not for me to prompt him.
I genuinely believe that men just don’t have the inclination to keep in regular contact once they have another woman in their life. Women form bonds differently and I think are more biologically programmed to nurture a number of relationships simultaneously, perhaps to do with the maternal instinct? Women, biologically, need to be able to do this to be successful mothers.
Just my view based on very ancient ideas! When all is said and done, we are still wired into our very basic natural instincts. It’s why breastfeeding works so well - for sleep, health, protection and forming unconditional bonds with your baby, and why harsh unnatural treatment of babies (cry it out for one) can be detrimental. Going with your instincts and against what society expects can sometimes be far healthier and make for a far happier life for you. The same goes for different relationships.
Men are just lazier at relationships. The wife usually finds the MIL to be a pain (no blood relation, no lifelong family history, just a woman that’s been inherited through marriage) and therefore won’t try to encourage much contact. Not a popular opinion, but I view my MIL as some random woman that I now have to incorporate into my life and I don’t think I’m the only DIL who feels this way. It doesn’t matter how nice they are, it’s often an awkward relationship even on the best terms.