Yeah I agree. I mean, I love the Woods theme but TBH it should only be used for Halloween since it's too spoopy. I'm hyping for the Winter theme though!
It'd make the woods lose at feel and make it essentially pointless. That's why it only shows up when the woods is active, to account for the event. Making the woods a naturally recurring theme would basically be like making pierrot an actual collectible after the April fools event. It'd lose the point of having it in the first place.
It wouldn't make sense to have it as the permanent theme, but I think what people want is the option to be able to choose it. I mean we only have the choice between the normal Bell Tree theme and the generic forum one that you could find most anywhere. It's a variety thing.
That said, while I would like The Woods to be an option just for variety's sake, it would indeed defeat the purpose of having it for Halloween.