There's a very British mentality about the bloody minded enforcement of rules, it doesn't happen in much of the first world. Many of the EU regulations we rail against are the UK gold plating the meaning to the maximum interpretation, not something the French and Germans do. I flew four legs in the US last month, a country knowing the price of lax airport security more than any, and the % of bags pulled aside was a fraction of the UK.
There would appear to be an algorithm at work to randomly meet a preselected random target of secondary screenings as a deterent, which when couple with those that actually need re-screening leads to a Hellish customer experience. I genuinely believe this has more to do with our own bloody mindedness than any genuine threat protection. It's "rules is rules or your out". The main pain point is that the main customers at MAN are exposed to different variations of airport experience at the other end of their journey and the comparison is shocking. One only has to look at Glasgow to see how it can and should be done in the UK, meeting DfT rules without the sheer horror of MAN T3.

Perhaps the technology at MAN is so poor that they really need to handsearch so many? Perhaps there is a danger and we should be worried? We'll never know as any incompetence can always hide behind the banality of "We never comment on security matters."