That's true, but you also know that if you withhold fees, you won't receive any education this term - you will be cut off from any provision. Schools usually have a time period in their contract, after which non-payment of fees results in children not being allowed at school. And of course, any relationship with the school will be ruined, even if you somehow managed to return later.
I don't think very many people plan to withhold fees in an obvious way, as the thread title rather goadily suggests. Even Op says she doesn't really intend to....I guess the thread title was to get traffic. Anyone who did, wouldn't just be making a protest about current provision in an attempt to get an improvement, but basically ending the relationship with the school and for their children. Most people really don't want to do that, especially now when finding an alternative would be rather difficult.
So I just take the thread as not really being being about withholding fees, but another moany thread about remote learning provision. It's another where people discuss what is a good way to deliver remote learning and the realities of it, along with discussion about paying for something you are contractually committed to, which changes during lockdown. It's not really about people planning to pay zero.
There might be some people who tell the school they can't afford to pay the full fee (or discounted fee which is offered) when actually they've had no change in circumstances. They might tell this lie if they feel really disgruntled and because they aren't actually willing to refuse to pay......probably because they know they haven't really got a leg to stand on. I suspect very few who can afford to pay have refused outright. They might have a feeling they would like to, and others might feel they ought to have a bigger discount (although when people think this through logically in terms of the costs the school is facing, being contractually bound and the school providing the level of service they expect in the long term,for their child, they might realise that again it would be hard to make a very strong case for this) than offered, but will either pay up or lie about ability to pay rather thN directly challenge the level of provision.
I do understand the feeling people have often initially had about paying a bill for thousands, when they are receiving something quite different to the usual. I think most people initially had the thought 'hold on, is this right to be charged X for Y'. But then, most people were able to think it through. They could see the circumstances are unique. They could see that they want the school there in future for their child and they paid X in previous terms for X and if they want X again in future for their child, they will have to pay what the school is saying it requires and that the school will be providing what it can, even if it can't be the same as usual. So they shake their heads and feel a bit disappointed but realise it's really no-ones fault and that its just on elf those things......and get their metaphorical choice books out. And most also accepted that what the school is providing is evolving, because most know that it takes time to develop a really good system. Most schools managed to wheel something out before Easter, but that was very hurried, and then worked very hard over Easter training staff and modifying systems and work, som something rather different emerged after Easter and no doubt many schools will be further modifying in light of experience and feedback. Most parents can see that is inevitable and manage to show some patience. Isn't showing some patience necessary in lots of areas of life at the moment, rather than s shouting of 'I'm paying, so you deliver what I demand right now'.