Why is the £50 note rare & barely used?

Like, what’s the point of its existence when that denomination is difficult to come by since ATMs don’t disperse them. I mean, will they still refuse a £50 note when paying for a £45 purchase? They go full counterfeit detection mode just because an individual has it despite that being the real one (not fake). Also, why does the Bank of England keep printing more of that when they know people barely use it anyway?