Good teachers have a thorough understanding of what they are teaching. My guess is that most teachers in UK schools don't. From my undergraduate degree, many years ago, the only people who went into teaching were bottom of the class. For example after a 3 year maths degree a guy who was enrolled in a teacher training course after graduation did not know what a linear function was (y = Ax + C simply blew his mind). It's hard to attract talent because at best it's a lifestyle job that is kind of awful while you're doing it where the pay is low and the expectations are low, but gives you 1/3 of the year off as compensation. Unless your primary concern is a job that fits around childcare, then teaching is not the job for a capable person (pragmatically). Also 80% of the concern in schools now is "safeguarding", which from what I can tell assumes that everyone is a constant threat to everyone.

Learning is not supposed to be fun, the way playing games is supposed to be fun. Sitting alone with books for hours at a time and thinking on problems has a certain joy to it, but that's hard won. Kidding children into thinking that it is, is a huge disservice to them.