Everything is not easy to everyone!
Why do some become more Calvanistic in their viewpoint and others become more Arminian? Probably something to do with our sin natures, which accord to us human pride, and lack of complete understanding of spiritual things.
We see through a glass darkly, as Paul put it. We cannot see clearly, in this life, all that the Lord has revealed. It is ourselves that are lacking not His revelation.
I am not saying the C is right nor am I saying the A is right. I think the truth lies somewhere between the two, though personally I lean more to the C view.
Why does conversion seem to come easy to some people and hard to others? I think a lot of the reasons are the same. Any way you slice it, we are tainted by the curse of Adam's sin and that curse causes more decay generation by generation. Of course, that is probably a different thread to discuss that point, but people do learn things at different speeds, some have a greater helping of pride than others, some have an easier time trusting than others; there are a wide variety of differences in each person's makeup that will impact their views on many of these subjects.