Take a phalaenopsis growing in straight sphagnum and move it into S/H culture, and it's a major step up for the plant, as it's just as moist, but much airier. Move a plant that has been grown dry in coarse bark, and that IS a major change.
The simple fact is that the conditions in a pot of fresh bark and that in a pot of the same bark that's been in use for a year are different. Roots that grew more recently in the old bark will fail sooner than the ones that grow in the fresh bark. Fact of life; just a matter of degree.