I agree with what some pp have said about, 'out of sight, out of mind'. The fact that he is friendly when you do speak, to me, indicates it's not that he doen't want contact, it just doesn't cross his mind and if there no set purpose to talk the chat won't last long.
I do think this tendency is more commom amongst men. (Not all men and not just men, but more likely.)
My husband was like this when we got together in our early 30s. His dad had a quiet word about phoning more regularly. He has got a lot better since we had children and calls once a week.
My brother is also pretty rubbish at ever being in touch with my parents and me. When I raised it once he was genuinely surprised he hadn't spoken to any of us for months.
I think the approach of 'I'd love a bit more regular contact rather than why don't you contact me' is a good suggestion. Can we have day/time whem we do check in and/or setting up a family whatsapp.
Cld one of the siblings have a word too? I've spoken to my brother about making more effort with our parents, esp as they're not in such good health now and to be fair he has. Probably not hugely protracted conversations, but he does check in more.
From your post it sounds like you're being considerate and don't want to be overbearing, but wanting regular contact with your adult children isn't at all unreasonable - assuming a healthy background and no legitimate reasons for LC or NC - but you might have to spell it out more. Good luck.