It was built by the Qin Dynasty, which despite being called “the first unified China” was a fraction of the size of modern China. And was built in part to keep people who are also now Chinese, and not just Mongols, out of “China”

And it also didn’t last, it was fractured whem that dynasty fell.

Other than distant genetics, they have as much in common with modern China as the Greek government does to the linage of Ptolemy.