I have not known very many grown adults who have changed a strongly held belief. Even if they are shown proof that their belief is incorrect and that there are compelling reasons to change, they will still hold onto it like their life depends on it. The main reason that I can think of as to why this happens is pride.
If someone has defended their belief for several years, even arguing with family that their view is the correct one, then they are highly unlikely to easily change. Doing so would be admitting that they were wrong. Also, their lifestyle may have to change if part of it was predicated on a belief that they now know was in error.
I’ve had to change some of my beliefs before and it wasn’t easy. I was so sure of some things that I would have bet my life on them and it was partly because that what I believed was what I had always been taught. It required an adjustment period that was quite awkward and it required me actually seeking the truth instead of aggressively defending my opinion. (By the way, one of the major changes for me was eschatological in nature and it took me a while to become comfortable with it.)
My prayer, then, is that more of us would spend more time contemplating why we believe the way that we do and desperately seek the truth until it is found. I’m not saying that we need to be wishy-washy in what we believe. What I am saying is that we need to know why we believe the way that we do and not be too stubborn to change if the need is there.