I don't condone putting ambient tracks at the end, but really from what I've heard these tracks are just a vague attempt at making something downtempo. Ambient music isn't just "psytrance at 80bpm", it takes talent to make a low tempo track interesting. And being a talent at psytrance doesn't automatically make you a talent at every other electronic genre.
Can you give me some examples of ambient tracks at end of psy/goa albums that you find to be good? I'd like to give a listen, maybe I haven't tried enough albums. But what I've heard so far isn't that interesting really, except maybe for some AP stuff.