(If you want to know about the more in-depth stuff, then our sister site, How-to-Geek, has a great explainer on XLR mics.)
To put it simply, while the same kind of tech is found inside both USB and XLR mics, XLR is just more capable of transferring high-quality audio signals.
This is the big one and an area where there is zero competition-even mid-range XLR microphones can sound better than high-end USB ones.
