Not necessarily. It can also be a shift away from receptiveness to evidence.

I haven't kept careful track of the paths taken by all the people I've known who've converted from theism to atheism (I sometimes wish I had,) but I have noted that it often comes as a result of taking their religions more seriously and seeing them as sets of beliefs with real factual implications, which should pay rent in anticipated experiences, and then realizing that they simply don't match up to reality. For some people, deism represents a retreat from ever having to think about the implications of their beliefs.