I'm not sure what would cause a typical stem plant to stop producing aerial roots. It isn't even obvious to me what the aerial roots are used for by the plant. All plants, even terrestrial ones, can obtain ferts thru the leaves, so aerial roots aren't really a necessity for them. Underground roots can be used to anchor the plant in a current, to feed nutrients to the plant, or some other use (?) Several years ago I had a 120 gallon tank, with soil layer under the gravel substrate, high light and very limited fertilizing and CO2. My stem plants still produced aerial roots, even thought I used Jobes sticks for undergravel fertilizing.