John Little's book max contraction advocates very brief full body workouts( a minute ) and doing so only once every week. He reasons that a muscle needs only to be flexed in its fully contracted position w/ high intensity a few seconds and adequate recovery time to adapt and grow. Multiple sets for body parts and full ranges of motion aren't necessary and further stress the muscle youre targeting. John Little worked closely with Mike Mentzer on high intensity training. and Mike Mentzer trained dorian yates under its principles.

why dont many more people train like this if its so effective and convenient?

A possible first step, which is what they're describing: Weekly, full-body workouts is going to have unimaginable consequences to someone's body who's unfit.

It gets harder from there and a lot of sosuave's good advice chooses the middle ground: Advice that helps people who are just starting out or who've already climbed that rung of the ladder. Its universally helpful, as a consequence beginners might assume ss overcomplicates things.

The main thing you must remember is that all of the sane replies come from people focused on CONSTANT improvement, so it can dwell outside the beginner's first few weeks.

I was initially taught this principle at uni, and I tried it for months only to conclude it doesn't work for me.

Still, I know a few guys who swear by it.