Well, the squat is considered a major movement, o it isn’t a huge surprise that people do it often when they go to the gym. Another reason is that the squat does target a vast number of major muscle groups. Think about it - something that’s been around for as long as the squat has must add some value to people’s lives.
Here are the muscle groups that the squat works:
- Glutes
- Hip
- Thighs
- Vastus Medialis
- Vastus intermedius
- Hamstrings
- Quadriceps
This is why the squat is one of the main movements that you see people do in the gym - it works a ton of different muscle groups. However, there are other movements that can replace the squat (that work the same muscle groups). Which leads me to believe that the sheer popularity of the movement is why others have stood with it for so long (also, why not do something that has been proven to work?).