Yes, OP, there are amazing, specialist foster carers out there, but there are not many. I have two children with SEND and I've been told that the nearest suitable foster care placement would likely be over a hundred miles away.
One of my children has already spent time in psychiatric hospital and if I became ill and disappeared into hospital for even a couple of days, she could take years to feel safe and secure again, during that time she would be a huge risk to herself and others. This may well be true for your children but decisions are made on the assumption that non-SEND children are neurotypical, and reasonably resilient. Obviously children vary but overall SEND children are more severely impacted by equivalent experiences.
I feel for what you have been through as a family. Parental death is devastating for children to experience and of course you don't want to die and your children go through that again. But at least the basic physical care needs of your children, in that situation, could be met by the majority of adults.
As parents of SEND children, there are much fewer possibilities of places that could meet their care needs, if any. A move of over a hundred miles away would be devastating for them on top of parental illness/death. I have no family members or friends who could cope with my children. The trauma impact could be greater due to their lack of understanding. I have three children and there is no one family or institution that could keep them together due to the variety of their needs.
But the government aren't doing this because they give a shit about they are doing it because they would rather pay me £67.25 a week than upwards of £750 a week for specialist residential care. Whereas most children could be accommodated for much less