A few years ago, this area was infested with gypsy moth caterpillars.
Some areas had it really bad, to the point of entire houses being covered.
I was lucky, they only keyed in on the oak tree on which the birdhouse was affixed.
My guess is that they filled up the birdhouse, which explains no birds since then.
I’m also guessing that it became home to other bugs/insects and one of those pileated woodpeckers made holes big enough to fit into.
Mission accomplished. The holes are 5-6 inches in circumference.