Sherry for many it is a starting point on their journey to fully dress one day, I started out that way partly because at that time I did not know where things would go but as time passed by I dressed more fully. And now my freedom is getting better and the days of drab because of who and what are getting less.
But also for many DADT situations, neighbours and such like put constraints on what some can do, sure they no doubt would want to explore things further but circumstances prevent them so for those (or many) underdressing is their own way of connecting with femininity.
To answer your first line I would have thought that if circumstances permitted those that underdressed probably would go further. I also think that we should also factor in a persons financial situation that just maybe (and I might just be a bit wrong on this bit) they cannot persue mor expensive items, dresses and such like.
