Somewhere around you house was a way in before the cold set in. At this point they are not coming in but moving around and that is what you are seeing.
I believe that homes that use multiple entrance & exit doors will see more of these as you open up more avenues for them to get in.
We have chipmunks and mice but no stink bugs and we have a drafty old 1790's home.

We hate this house and can not wait to get ride of it but, no stink bugs.

As mentioned these buggers are slow and patient, a vacuum will just give them a temporary home. Someone else posted, pick them up and flush them then they are gone for good.