We were not at all surprised that they decided not to nest in the box despite the hard work. After all, we have lots of trees with great cavities for nesting and this nesting box is relatively near the house. It is most often used by chickadees.
The other day I saw a gray bird entering the house. On a limb above it sat a Tufted Titmouse. Interesting.
As I kept observing, another titmouse (I'm assuming a female since they do most of the housework) flew into and out of the house.
On occasion, she removed something she had brought in. Perhaps not the right design for her decor.