Because a number of competitive shooters use a form of this stance - some more than others. It trickles down and evolves to some really exaggerated forms seen at your local range or on YT. It is the training du jour that requires a handguard that extends near or past the gas block (so you don't grip the barrel) and benefits from a more vertical grip angle. A person is fully facing the target, with your feet in line, shoulder width apart. (As opposed to the more traditional angled to the target with one foot in front of the other.) When seconds matter, shot strings are quick, and this stance doesn't have to be held forever, a form of this may be able to shave precious tenths of seconds off your stages. You just point the bullet hose where it goes - haha. Oh, and it's AR and similar only - most people don't want to do this with an AK - haha.
OTOH:
If you're attempting a freehand shot and want to sling up
If you're passing through doors
If you have to hold the stance so long that muscle fatigue affects your shoulder, elbow, or wrist
If you want any situational awareness on your support side
If you get annoyed by seeing your thumb in your sight picture
Or if you have a 16" carbine with a regular, double heat shield plastic carbine handguard
The c-clamp may not be for you.
Don't get me wrong, it is good for it's competition purpose, but not so good for everything.
Also, training videos don't just sell themselves. There has to be something new and novel that requires the purchase of additional accessories. Like a new handguard, grip, VFG, safety selector, hand stop, etc.