I think it's a numbers game. There are just so many more kids out there now with SN of all types: partly because medical science mean kids who would have died now live but with high-need disabilities, and partly because of the increase in things like ASD and ADHD which isn't just down to better diagnosis. Only anecdotal, but my mum says she simply didn't see kids with mild ADHD and ASD in her classroom - well, maybe one or two, she recognises now what their behaviour meant - but compared to the numbers in school now, very few. So the total cost of supporting kids with SN has rocketed.
At the same time, the inclusion agenda has pushed kids into mainstream which has taken the support and funding decisions away from people who chose to work with SN for a living and put it in the hands of education departments and governing bodies. So it's not a question of can the Special School squeeze another child in, it's a question of get a new LSA or replace the unsafe bannisters in the Science Block.
Plus the more kids there are in mainstream who shouldn't be there, the more disruptive it is and the harder it is to give them differentiated learning and still carry on with the rest of the class. So children with disabilities in mainstream are in a far more hostile environment: they are a financial burden and a burden in the classroom.
At the same time, the legal rights of children to education & therapy have been tightened up greatly, partly because the internet age makes it easier to know your rights and middle class parents in particular will take LEAs to court and so the law has been clarified by test cases. On paper their rights are clearly better.
So, I think the balance and the mechanics of it has shifted. It used to be about separate schooling where the family had to trust that their benevolent special school knew what they were doing and had the child's best interests at heart - far more like the NHS in this regard, and like the NHS quite often these schools justified parental expectations though if they didn't there wasn't much you could do. Now parents are much more empowered to fight for what their children need, but the problem is that it is only by fighting - and quite probably poisoning your relationship with the school - that your child will get anything approaching what they are now, in theory, legally entitled to but which aren't in the schools' interests to provide.
That's very much an education answer. The situation for NHS and Social Care is simpler. With Social Care it is only about money. Our ageing population take a vast amount of cash from Social Care and not a lot is left over for the increasing number of kids with disabilities. Also less special schools means less residential schools so more burden on families. With NHS it's hit-and-miss: the miracle life-saving stuff is improved beyond recognition, of course, and very often there seems to be budget for expensive scans and operations. But what kids with disabilities need on a regular basis is therapy and the budgets aren't funded to provide it for increased numbers. The Physio, OT (occupational therapy) and SALT (Speech and Language Therapy) available to our children nowhere near meets their needs; it's one of the really big failures of the current system.
Hth.