Geez, I feel bad for the OP...
So many MNers totally jumped down her throat with "why does it matter to you what he does?" "What do you care?" "So, let the man do what he wants"
You guys are freaking lazy and a horribly opinionated but then again, I mean she is asking for your opinion so, ask a question, get an answer, right.
I get it. Many of us have to do things we don't want to do when we don't want to do them because we have to. Or we feel that we have to, we either have to (like work / school) or feel that we have to (relationship/family /friendship issues and expectations) and an awful lot of people put their own wants and needs last.
Like, if you just finished cleaning the house, doing all the shopping, planning the dinner, doing all the prep work, you're absolutely exhausted, and all you want to do is take a nice warm bath, or put your feet up cozy and watch some dumb TV....
Then all the sudden some family obligation comes out like oh we have to go and visit so and so or oh we have to go and do a walk or all we have to do this or all we have to do that...
And you really really don't want to and you really really feel that you'd like some me time and you really really feel that you deserve a break but you also feel that you don't deserve to let the family down, and that you don't deserve the right to oppose, so you do it and then you resent it. I think a lot of people are feeling that. The resentfulness, so they say, "leave the man alone if he doesn't want to walk don't make them walk What do you care?!"
But I agree with her and a few other posters that said look, don't be so hypocritical. When the plans are being made to go for a family walk with the young children, and you say "yeah this is a great idea let's do it" And you claim to be an outdoorsy individual, but then when it's time to put on your shoes, he says no I'll just stay here instead. And no he's not staying behind so we can clean up and no he's not staying behind so we can wrap the presents and no he's not staying behind so we can do some other work so that other people who are enjoying a bit of a break taking a walk don't have the extra work when he comes back no he's just doing it because he doesn't want to. Sorry. Selfish.
When there are young children involved and you are trying to get them to go out for a nice walk on a beautiful day (And yes I would say blue clear skies on a gorgeous Christmas season day is gorgeous weather) And you're trying to instill the idea of doing things together as a family especially outdoor things that involve activity not just sitting around everybody doing their own thing staring at their devices... It would be nice if everyone made an effort. Little kids are only little once. Few years from now they're going to want to do something else probably video games or maybe hanging out with their friends, not going for a family walk. Will the grandfather be regretful that he didn't go for walks with them when he had the opportunity? Probably not probably won't even think about it. But, you only get this time once. You don't know what tomorrow is going to bring. So, get off your ass, go for a walk, and enjoy yourself.