Thats not bad luck or overuse, thats selecting the wrong horse for the job. The physical build this particular horse was bred for and born with aimed at WP does not allow him to be successful over fences and that can result in physical issues. Seen this quite a bit over the years.
Not their fault, betting they got some bad advice when they chose him for an H/J career…probably from somebody who should have known better or didn’t know what they were talking about.
This being COTH and just in case…QHs come in all sorts of shapes and sizes. Some are quite suitable for H/J others not so much. Have to pick one that can physically do the job you want it to.