[RJT]

This might explain things. Others can confirm or correct me.

The basic disagreement between Catholics and other denominations regarding Mary stems mostly from the following:

Catholic beliefs stem not only from the Bible. We use sources in addition to the
Bible - for example early century Church Fathers (more or less the early theologians) - our doctrine did (does) not stop at the Bible. As you can see from my previous post, it is as recent as 1950 that we had a “major official stamp” on the Doctrine of the Assumption of Mary (this was not a new belief, just formalized so to speak).

Most (all? - don’t really know) Protestants take their doctrine only from the Bible. Different denominations interpret various parts of the Bible differently ( from each other and from Catholics).

Mary is not mentioned in the Bible much.

To answer your question - why does anybody care? I really didn’t know it was such a big issue. I mean of course it is a big difference in opinion and relatively speaking a big difference in Theology. But I don’t think most care that much. I wouldn’t put it at the top of the list of thing to discuss with those not very familiar with Christianity; if that too is what you are asking.