Simply because all kids nowadays want to train a few minutes a day, a muscular group a week and believe they'll become like bodybuilders with a minimum of efforts.
The only way to build muscle naturally is at least 2-5 hours a day, each muscular group 2 times a week. Like we were doing before 80's
There is no miracle. The less you train, the less you progress...
that's too general a statement and dangerous advice!
my own experience: yes, I did so when I started out. at that time I developed the mind/muscle connection as a basis for targeted intensity.
after 2 - 3 years, however, I hit a plateau, as I was
chronically overtrained. only when I started to cut back on the frequency of workouts (not the intensity), I started to grow again (we are talking here a few grams of muscle a year - not kilos).
now, as I am 42, I need way, way more recovery time than 20 years ago.