Why didn’t the Gracchi brothers figured out (or failed) to carry out military reform and thereby secure the support of the army?

The Gracchi became tribunes because they were closely associated with the Roman plebs. That is why they could not have close ties with the commanding staff of the army – at that time he consisted of patricians.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.