Orthodox Judaism, like any belief system or community, has a certain set of values. There are many people who, either by temperament or ability, are unable to comfortably fit into a community based on those values. I believe that the gap between Orthodoxy's values and peoples' ability to conform to those values is the primary cause of people leaving Orthodox Judaism or having difficulty within it. I also believe that some of these values can be broadened to accept more people without transgressing Orthodox Judaism's fundamental tenets while others cannot be changed without ceasing to be Orthodox Judaism.
In other words, Orthodox Judaism can make some changes to increase retention without losing its essence, but there will always be those who simply can't fit into a community that's based on Orthodox values.