It has a lot to do with the fact that we humans seem to have an instinct that fights against any cry that claims we are incorrect.
Under normal circumstances it is important to have a firm self-worth, to trust in fundamental axioms we have come to accept as true, and to avoid being wishy-washy lest we never move forward. While it is important to have fail-safes in place that can aid in keeping us from deluding ourselves, it is equally important that we don't second-guess ourselves into an existence of immobility.
Even in simple and relatively unimportant things we can be stubborn about what we believe and refuse to admit we are wrong about something. We've all been guilty of it, and we are neither proud of these moments in our lives or quick to admit and speak up of these times. Even now, outside of the JWs, we all hold steadfast to our new convictions. We all have different viewpoints now, and we cannot all be right even now this side of the Watchtower, but I am sure we each, individually, believe we are.
To a degree this is normal, even healthy. But in a system like the religion of Jehovah's Witnesses it becomes a self-consuming muck of personal judgment, guilt, and a desire to do what is right as much as to be in the right.
So people who are emerging from the cult can and will sometimes speak out of "both sides of their mouth." The battle going on inside to fight this instinct occurs differently in each unique individual, and for some it comes out as condemnation for the JWs one moment and praise for them the next.
We might be convinced that what we are witnessing is individual "support for an evil cult," but we can be wrong. Entrenched ideas don't disappear overnight. Some come out habitually, some slip out without notice, others get stated becuase the person is flip-flopping on where their allegiance lies. We can't always think that what we are witnessing these people doing is what it appears to be on the surface. If anything, our experience as JWs should teach us the truth that we cannot always trust ourselves and our own judgments about things all the time.
What we believe defines our identity and our understanding of the universe and our place in it. When what we believe is in flux, the comments that emerge are equally in flux. People can't always see the way before them because, whether in a cult or not, all people can be experts of denial.
Remember, it is easier to admit that the religion of the Jehovah's Witnesses is wrong. It is hard to admit that we wrong for believing it and staying with it as long as we did.