taxpayers confronted

SO MANY ______ THAT _______ is a construction that you may have seen in grammar guides, and can be perfectly grammatically correct. It's used to show cause and effect structure. For example:

There were SO MANY people at the party THAT I had to leave.

This is another way of saying "BECAUSE there were so many people at the party, I had to leave."

In this sentence, there is no cause-and-effect relationship. The taxpayers confronted many changes, but that didn't cause anything else to happen. If we reword option E the way I did above, it would read "BECAUSE taxpayers confronted so many changes at once... confronted them." That makes no sense! Because there is no cause-effect relationship, the SO MANY / THAT construction doesn't work.

What we want to say in this sentence is that taxpayers confronted more changes than ever before. "Never before had they confronted AS MANY AS..." is the correct construction to express this.