Why do Protestants accept the inerrancy of the canon, while rejecting other decisions of the Roman Church? Why do Protestants accept the inerrancy of the current canon of scripture but reject many of the other decisions made by the Roman Church at the time the Bible was being canonized?

Take the Council of Laodicea, for example. Canon 60 of the Council of Laodicea states the books that are allowed to be read. Revelation was not included at this time, and some books were included then are not included today. Also, the Council of Laodicea stated things like marriages and birthdays are not to be celebrated during lent (canon 52), and Christians should not dance at weddings (canon 53). So it seems like the council's decisions on some things are just simply ignored, while others, especially the canon of Scripture, are readily defended. Why?
To answer your main question: The Council of Laodicea, being a regional council, would only have been binding on the Faithful living in the region (specifically, on areas that were represented by their bishops). Being only a regional, and not an ecumenical council, it is not binding on all the Faithful.

For your question about scripture, the answer is a little complicated. Wikipedia summarizes it well, but the important point is that we have points at time where we know Canon was already considered settled, which was certainly before 400. It is harder to point to the moment where it actually was settled, although the broad strokes clearly had been in agreement for a while.