Some variegations are infact caused by viruses in the plant, but in the case Aeae it is not viral, but a somatic mutation that has taken place that causes the plant to become chimeric. The reason it cannot be successfully mass tissue cultured (there has been a few successes, but its still easier to grow from pups) is because the variegated tissue is spread across the meristem in such a manner that when you take a small piece of tissue to culture, it is very difficult to get all of the different chimeric tissue colors in one small piece that will continue to grow together.
Agri-Starts did infact produce 7 stable variegated Aeae from tissue culture over the course of 4 years, that of course was not economically feasible at all so they gave up.
I also know of some successful tissue cultured Aeae that stayed stable for 4 generations only before reverting to green.
Growing bananas in Colorado, Washington, Hawaii since 2004. Commercial banana farmer, 200+ varieties.