Op, your message isn't true for all mums.
I have two adult sons.
One has a partner the other split from his 6 months ago.
We see and hear from them loads during the week.
Dh is working on a project with ds2 in their spare time and ds1 joins in.
With ds1 me and dh go on long hikes at the weekend and during an evening in the week. He has two dogs and I have three so we do this all year round.
All 5 of of us go to quiz nights, meals out, the theatre, pub etc. Not always all of at the same time, but sometimes for a particular event.
Ds2 drives past our house on the way home from work and will often pop in for a brew. He won't always stop long mid week as he has a partner he has to get back to inless she is working away.
Both lads are buying their own home and have lived away from us for years. One left at 17 and came back for a few months and left again. Other son left at at 21 and started buying his home at 22.
Ds1 is the organiser and always making plans and ds2 is very prote time of me.
Op I'm not sure whats happeed that your kids dont stay in contact much, but do you reach out to them eg face time them and ask about their lives and sound excited and interested by what they are doing.
Ive reduced contact with my mum as for decades she will talk about herself in the phone and then say ' anyway, Ive got to go, glad you're ok' without even asking if im ok. She never calls me unless it's bad news. Its not a new thing she's been like this forever and still holds stupid things I did in my mid teen yeas against me ( im frigging 60!!!)
Op, im not saying you've done anything wrong but have you done any self reflection. Maybe youve got selfish children but are you sure you are not negative, critical or judgement of their choices. I know I always try to think before I speak, especially with one of them who reads too much into things I say sometimes.