They are often too small overall and contain crevices too large. Sometimes a critical detail is omitted, such as a landing plate. Usually these boxes cannot compete with a modern design, even after being upgraded by a creative hobbiest. Bad construction is a different matter, usually the box can be successfull after some paint, caulk, extra screws, and extra roughening. A single chamber box.
Bats simply prefer larger structures which offer more stable temperatures.
Factory smooth interior crevices. All interior wood must be roughened for bats to readily cling to. Some commercial boxes staple screening to the inside of the box which may eventually fall off. Roofs without shingles may last only a few seasons, once the roof is compromised the box will be incapable of retaining heat and fall into disuse. Nailed together with unsealed seams.