Cold for me is not an issue (unless we're talking about the -10F or colder kind), and in some cases it's a feature. I can't stand being boiling hot on a long hike, and going out in the winter can be just the antidote to that.

It's also a lot easier to tolerate when the reward is silence and solitude.

To your point, not every trail will be accessible in the cold, and that is certainly a factor. But most parks have trails that are perfectly hike-able in the winter, and one of my favorite recent hikes was a pre-dawn snowy hike to Dream Lake at RMNP. I was the only person up there, got to watch an incredible sunrise reflecting off of the recently frozen lake, and then enjoyed the best tasting coffee I've ever had.

Not for everyone, but can be an amazing experience.

It was not that cold right after Thanksgiving, except at higher elevations. My friend and I hiked amongst the hoodoos in Bryce Canyon in the sun. It was pleasant enough not to need a jacket.

But as I said, once snow falls, they'll either close a number of the trails (Bryce Canyon), or they'll keep them open but you'll be walking on ice (Arches).

I saw Arches only when there was ice, and it was still totally worth it!