Hiya Yeah it's down to mainly health and safety but also to ensure the law and rules are followed (trust me we don't all agree with them and some are badly worded).
For example - someone mentioned fake tampons - you can also stash drugs in them or explosives. If I see Tampax in a bag I will ask her to remove them and randomly check inside them, rattle them etc. We do replace them with our stock tho.
With concerts we pay a lot for them but some concert halls have added insurance and even additional support needs due to crowds, alcohol consumption and bringing in stock etc - clean up crews are very pricy.
Its honestly amazing what can be smuggled in and where (yup and I also mean people body packing, pretending to be pregnant (we have safe zones for pregnant woman incase of issues etc) and police will randomly do body checks and sniffer dogs depending on concert or event (T in the Park for eg)
We have to follow legal rules first and obey the ticket rules second- I've had great fun snapping season ticket holders cards up at football since they broke rules.
Every event is different, every minute of that event is different.
Just be safe and best advice is to listen to us as we are there to help you not curb your fun. You when buying tickets agree to the rules as a contract- break those rules and you can be banned.