I've done my fair share of CCTV trawling, including several weeks worth for a murder investigation and its incredibly labour intensive. Someone else would soon moan it their bobbies were spending their days sat in front of screens instead of patrolling.
Its a question of resources, and they simply don't have them. They need enough lolly to do all the tasks they are called upon for, but they simply don't have it. The fault lies with the government.
As an aside, the public expectation of cctv footage is unrealistic. Its a very poor detection tool.