Lack of resources vs increase in demand, plain and simple. I see it first-hand, the level of demand on the police is growing and yet they're somehow expected to do more with less. England and Wales have 20,000 fewer police officers than it had in 2010, and significantly fewer police staff too. Specialist units/teams are being scaled back, for example Hampshire is set to lose 15 dogs / handlers, 20 Roads Policing officers, 4 firearms officers, 16 officers from intel, 12 surveillance officers and 27 support unit officers due to budget constraints this year. That's despite the supposed uplift in funding from Government for firearms/CT-related roles.
It doesn't take long for criminality to realise this and use it to their advantage.