It's not only monetary value.
Every child needs to be educated. There are limited school places, both state and private. Some schools are better than others: both objectively better and better for that child (eg size, location, philosophy) Every parent is responsible for getting their own child into the best school available to them at the time they need it.
If a parent has accepted a private school place but then they're not able to use it, then their child still needs to be educated. In almost all cases, the state school place is a good backstop for the different things that could happen in 6 months:
1.job loss. No, people don't only put their kids in private school if they're so rich that they have 7 years of school fees and living expenses saved up beforehand
. They make sensible risk-based judgements.
If I had no job at a time that my child was about to start, that might change that risk-based judgement
2.the school closes - as 4% of private schools have in the last year thanks to VAT. It's a risk parents must consider
Any sensible parent will consider both those possibilities. In only a very small number of cases will neither of those risks apply.
Not only for a child with SEN, for any child.
A private school parent is not selfish to wait until a few weeks before term before giving up their fairly allocated state school place. They're just thinking clearly and taking a risk-based approach with risk mitigation and a back up plan.
The many posters on this thread demanding that parents intending to send their child to private school in September - currently 6 months away - to 'reject the state offer asap' are giving terrible advice to other parents. And worse, putting judgement and social pressure on them to do it.