[Dan]

Why he has so many back surgeries?

The spine cannot take it

It happens when the initial surgery was not properly done. Subsequent operations were necessary to rectify it but in doing so more complications arose due to the intricacy and complexity of the spinal cord system. It's not like repairing a car engine where you can replace bolts and nuts with ease. After too many tries they must have reached a dead end when the spinal system decides to shut waist down. The spinal cord is like a main cable supply with many fuses along the route to other organs. Once blown it cannot be replaced and those parts affected cannot function ... paralysed

Just a layman theory