The reality, often ignored, forgotten, denied, or unknown by Protestants, is that the Protestant groups separated themselves from the Catholic Church. Luther, Calvan, Zwingli, the Church of England, etc… all those folks were Catholic until they chose to leave the Catholic Church. Protestants out there today are still, knowingly or unknowingly, part of groups who have voluntarily separated themselves from the Church.
It’s a little like this. You work for GE, and your family has always worked for GE. You quit, and start your own similar company, GL. A hundred years later your descendants, still working for GL, walk into a GE office and demand a paycheck. They won’t get one because they aren’t part of GE, even though they do a lot of the same things in GL. They have to get hired and trained and start working for GE before they can expect a GE paycheck.
The analogy is far from perfect, of course; the Church is a lot more than a business and the Eucharist infinitely more than a paycheck, and this doesn’t address the issue of receiving while otherwise properly disposed. But it may help some people understand the Catholic perspective, even if they disagree.