This is a terrible lack of agency on the part of the parents.
The parents knew what was happening. They knew how it was affecting their son. They claimed to love their son, and yet they took no serious action to solve the problem other than asking someone else, the school, to solve it.
That is low-agency behavior.
If you are a parent, you are the protector and defender of your child. You do whatever is necessary to keep that child safe.
If that means removing the child from the school, you do it immediately. You do not wait for permission. You do not wait for someone to suggest it. You do it, and then you figure out how to make it work.
Or, if you want to keep the child in school, you make sure charges are brought against the bullies who assaulted your son. Or you go and resolve the situation yourself.
What you do not do is allow it to continue being your son’s problem until he cannot handle it anymore.
These parents had many opportunities to intervene and protect their child. And from the child’s point of view, what may be even more disturbing than the bullying at school is the fact that his parents made him keep walking back into it every single day.
The extreme disappointment in your parents’ actions, the realization that they refused to protect you, has got to be much more devastating than the fact that some stupid kids were bullying you.