Why didn't the Orthodox and Catholic Churches switch to using the Masoretic text for the Old Testament when the Protestants did?

Historical accuracy? The Masoretic is +1,000 years older than the Septuagint Old Testament the New is based on. This assumption it's more authentic because it's Hebrew is a myth.

Here's what I don't understand--if Protestants think the Septuagint isn't accurate then how on earth can they accept the New Testament, since those writers used it exclusively?!

Because at that time (1500s) they considered the Latin Vulgate to be the only trustworthy source of the Bible documents.

Sort of ironic, considering the most of the Vulgate was translated from original language documents...but not surprising. Religion has a tendency to become "hidebound", a tendency to interpret tradition as dogma when that tradition is challenged.

(That's the reason we have King James Version Onlyists in modern times.)

FREE WILL...

They needed the wiggle room that poor translations provide.