Why do some players have regular issues with muscle tears, while others have none? Is it genetics, or can there be a nutritional element?
Genetics, nutrition, bio-mechanics, bad luck...take your pick.
If it is a similar injury over and over then quite possibly a bio-mechanics issue. Imbalance of strength across hip flexors, quads, hammies and glutes (a lot of younger players), compounding lower back issues (Gumby, Winders) causing over striding or poor running patterns.
Players work on strengthening the body to correct the imbalance and then work on running patterns to correct their stride length.