You just aren't letting new genes in the pool. Breeding is extremely complex, but this concept makes it easier to understand. In human beings, if the genepool in a given area has less than 100 ancestors you can count on genetic abnormalities and congenital defects (dwarfism, blindness, hormonal disorders, and heart defects).
Most every species has millions and millions of sections of genetic code that work coherently together to create what we see as this being. Among these millions of lines of code are a few thousand that are not functioning correctly, these are responsible for; disease susceptability, cancer, and general degradation (aging). But when off spring are created using the same genetics, repeatedly, you get a wide variety of results, but invariably you will saturate the genetic pool with genes that are damaged, altered, or nearly destroyed. It's like holding on to a clone forever, the DNA is being damaged all the time, just like our DNA gets damaged. But by forcing a feminized seed to make more stock you are exposing these genes to more carcinogens, and unavoidably you will piss in your own gene pool. You get me?
New strains are what growing is all about. Find that lady a man, who will treat her right, and you will find out that your heart was made to care for offspring. It's just nature.
Sincerly,
ILovePlants