It's not a loophole, it's a specific tax break for people cashing out of "small" businesses. ("small" means at the time you joined -- it can have grown huge since.) QSBS can save you a lot, but it can be a lot of work to file too. I ran up about $20k in accountant bills doing it on a complex deal. If you're selling founder or early-employee stock, ask your accountant if QSBS is right for you.
Seriously... not a loophole. Explicit tax rule. Just making it look like people are somehow taking advantage of the system. FUD.
The original is about a certain police force and was by Winston Churchill