It’s an interesting question, and one that I’ve heard before. I think a fitting bit of imagery that helps explain this is that of a mountain. Imagine “frumkeit” on one side, and “OTD” on the other side. Going up the mountain in either direction can be very difficult, but once you get over the top, sliding down the rest of the way to the other side is much easier. Yes, now that I’m not frum, I don’t think it would be very easy to somehow persuade me that I’m wrong (though of course, nothing is impossible). But on the other hand, it was also very difficult when I was leaving frumkeit – certainly not an easy overnight decision.
Note that this really would only apply to those who leave due to intellectual reasons. This would not be a fitting analogy for someone who decides they don’t want to be frum because they are angry, or trying to hurt someone, or simply want a less restrictive lifestyle. But again, for those of us who are no longer frum because we couldn’t make it fit with how we see the world, it often was a very difficult and excruciatingly slow process that led us to leaving, and would therefore be very difficult to reverse.
At least that’s how it was for me and several others that I know. Maybe someone else has a different way of seeing it.