7000 private school children have an ECH? in the state sector, England alone, the number is 517,000.
You aren’t comparing the right statistics. Just because a child isn’t in an independent school (and the 7000 is only the rough figure for independent MS, it doesn’t include independent SS) doesn’t mean they are in a state school.
According to the most recent government EHCP statistics, 575,963 children and young people in England have EHCPs. Of those, 248,016 are in mainstream school placements. (Although this includes 22,236 who are in ARPs/units within state MS.) Of those 247,016, 6,768 are in mainstream independent schools and 219,012 are in non-independent (maintained, academy, free) mainstream schools.