Hi Lois~
You must be brand new to the show circuit, since what you are talking about is pretty much what we've ALL been complaining about for YEARS from most art shows. It has nothing to do with Zapplication. It is the VERY rare show that sends anymore than a "you are in/you are not in" notice. There is nothing to indicate why, and it has been driving artists nuts for years.
The only advice I have to give is not to take it personally, and continue to try to get that feedback if you can. But, and this is the sad part, it is still very rare to know the why.
My own example of not knowing why: I was in a show for a couple of years in a row, and one year I actually got one of the awards, something that rarely happens to me, and so a nice surprise. The very next year I didn't even get juried in! Then the year after that I did get in. Why? Who knows? Juries change each year, so you will have different people looking at your work.. Different artists apply each year, so there will be different competition each time. The best we can do is create our best and send it out and hope we'll get in. It's a crazy way to work, but at least it is still an option to get our work in front of the public.