Hello,
The growth or lack of muscle size depends on many factors. You should check which one is the main reason for you.
1- Wrong training program: Not every training program works for everyone. Everyone has to implement their own plan.
2- Nutrition and rest after training and non-training days are very important in muscle growth. Night waking should be less.
3- Difference in muscle fibres. Of course, this difference shows itself at higher levels, but to some extent, the initial growth depends on it.
The above were the most important.
Good Luck1