I haven't switched traditions exactly, but something like it. I started out Theravada in my studies and understanding. I went to several 10 day retreats under Theravada teachers. Eventually I came into contact with some Chan and Zen practitioners, and learned some of their philosophy. I took the Bodhisattva vows and am firmly in that camp now. Now, as to your question about why to make a change?

The Chan group that I buddied up with put us through a program of academic training during which I studied the Lotus Sutra. Initially I thought the Lotus Sutra was nonsense. Why in the world would the Buddha deceive us for "skillful means?"

I'm still not sure I believe in the Lotus Sutra, but I don't think it matters. The Buddha teaches therein that the true path becomes clear when we gain enough wisdom, so to speak. Specifically, he said that all his teachings so far were just in preparation for the true path of the Bodhisattva. It's controversial to say that arhats are not done with their spiritual development, but considering the Buddha claims in the Lotus Sutra that becoming an arhat was just preparation for the Bodhisattva path...that means they are actually the same training. So whether Bodhisattva or not, the training and practice can be the same. If I become an arhat and see different, so be it.

Some people balk at the idea of a Bodhisattva making a vow to come back eternally, but that's not actually a vow that I took. Vowing to liberate all beings doesn't mean staying here forever. I have vowed to become a Buddha. As daunting as it is to come back for several mahakappas, that's ok, it's still a finite time period to achieve the greatest relief of suffering.