There are some wild assumptions here that are not correct. However there can be flaws in the governance system if people wish to exploit it.
Firstly, a few years ago, governing bodies were asked to reconstitute and co opt people with the necessary skills and experience to do the job. There is no way a governing body should be dominated by parents. In a 240 place school, we have 2 parent governors out of 12. We have the Head and 1 additional staff governor. The others have the required skills, as do the parents! It’s taken seriously.
You can complain to the LA governance section if the governing body doesn’t follow its constitution. The constitution is available from the school and isn’t confidential. It’s unlikely “dirty washing” will be in the minutes. You can ask for them, if course, plus agendas, but I wouldn’t expect them to be illuminating. The governors who resigned don’t have to explain themselves. They are volunteers.
That brings me on to training. Governors must be trained. It’s not obligatory but, if they don’t, how do they know how to do the job? The minutes should say what training has been done.
How do you know they agree with the Head? In fact, why shouldn’t they? The governing body receives (or should) a very detailed report from the Head for meetings and committee meetings. A good Head will give a lot of information and they are, in effect, the chief executive and responsible for the day to day running of the school. This is Not the job of the governors. The Governors are there to challenge and support and provide strategic direction but not to micro manage. If you can give examples of the governors agreeing with the Head, I can comment on whether this was appropriate or not. It may be the Governors all have different reasons for going. It’s not necessarily sinister.
Governors must challenge an ineffective head. In extreme cases this can lead to the Head going. As in every job, if you are deemed to be poor, despite being offered support and training, of course you can go through a capability process. Heads are no different.