There are increasing numbers of children with significantly impaired communication skills starting mainstream schools who don't have the skills to communicate basic needs.
Children at this level of development are far greater in number than appropriate SEN provision.
Not helped by SALT provision not yet recovering from the delays in 2020-21 so they haven't had access to early interventions to assist as young as possible.
DS1 was lucky to get early intervention in the mid-2010s which did assist with school-readiness. He wasn't non-verbal, but had difficulties in forming sentences together, particularly with the more abstract parts of grammar that create the flow of language.
For him, it wasn't the language delay that affected his toilet training as much as his sensory needs, self awareness and ability to switch focus. Even now as a teenager, he's not great at recognising hunger, thirst, or need for the toilet unless his focus changes at a transition point. He also has an iron bladder after 10 years of holding to avoid using school toilets.
Schools will know which children have additional needs/ undiagnosed traits and which children have lax parents not meeting their needs.
MN is abundant in additional needs parents because we find it a source of support which can be hard to find in RL.
Parents on MN are literate and looking for/ open to information to support their parenting. You won't find the uninterested parents who aren't inclined to help their children thrive on here by default. It doesn't mean they don't exist though. No one on MN will be here to admit that it's the school's problem to get on with (but there are teachers on the receiving end), but there are plenty of parents who've had difficulties despite their best efforts due to additional or medical needs (often not diagnosed for years) so the discussion naturally sways to a disroportion of SEN based viewpoints.