Outstanding schools can expect OFSTED if their results dip.
That can lead schools where the leadership is not overly confident to focus very much on keeping Y6 SATS results up at all cost. If they can just keep the results up, then all the other things that may be going wrong/leadership may be insecure about, can remain hidden.
And this again can lead to Y6 being an exam factory, all about preparing for SATS, all 'learning to pass exams' rather than learning 'stuff', highly pressured for the kids, and even cheating (which is negative for the kids as inflated KS2 SATS results will lead to over-ambitious expectations for GCSEs and thus pressure and a feeling of 'failing to achieve predicted targets' throughout secondary school).
It might even, in some cases, lead to 'weaker' students being 'managed out' (life just made uncomfortable for them, so that eventually parents choose to move them to a different school).
Also, a school that hasn't been inspected since 2008 has clearly had very good results every year for 10 years. Now consider which parents will choose to send their kids there, despite the lack of any recent OFSTED. There will be a lot of parents who really care about results (and a few who chose it for other reasons, like proximity; and a minority who don't care about OFSTED/results). Now what if these parents notice that learning isn't too great, their child is falling behind, or not doing as well as they'd expected? They get help for the child, private tutoring etc. That then means that the school may be continuing to be getting great results despite actually sub-standard teaching. So even the point 'well at least I can trust the school to achieve good results' isn't really a safe assumption.
DS is at a 'last Ofsteded in 2008 outstanding' school. Since the new head came in 5 years ago, nearly all staff (teachers and TAs and office staff, even the caretaker) have left. Importantly, not a single Y6 teacher has lasted more than a year. The results though have always been great. This implies, to me, that the great results are not down to 'fantastic teaching' in Y6, as there were five successive teachers who can't all have been fantastic teachers, so there must have been something else at play, IDK, pressure of some sort, but something clearly that made the Y6 teachers unhappy and caused every single one of them to hand in their notice by the time their class was sitting their SATS.
Also I can confirm that even a large number (>20% of school population) of consistently and exclusively very negative parent opinions on Parentview (see OFSTED website) will not trigger an inspection. The lack of inspections does not indicate that parents have been happy with the school.