I suppose I should be grateful that he enjoys spending time and playing with them, but he simply does not do it unless I actually suggest it, plus with a clearly defined activity.
Eg right now, they are playing cards at my suggestion. before that, they were all bored out of their mind, they had used up screen time and snapping and snarling. I suggested to DH why don't you teach them rummy and play, and they are doing it and sounds like they are having a lot of fun.
But this is a pattern. ANYTHING that gets done with the kids is at my initiation and suggestion- except with the important exception of homework help, where he has been very proactive with maths. But who does maths over xmas break? Thank g, the break will be over Monday.
I suppose I should be grateful that he enjoys spending time and playing with them
You shouldn't feel grateful for this, this is expected baseline behavior for a parent.
As for him, sometimes people are just bad a coming up with ideas. When I'm bored out of my mind, I have a hard time thinking of things to do. It sounds like if he's helping them out with homework without being asked that he is genuinely interested in spending time with them.
Suggesting ideas is better than my parent's approach. When we complained of being bored, we got a list of housework that needed to be done.