Much of it is that there is no standard in video security. Some places allow you to record it and save, but many are on a 24 hour erase cycle. Also up until this past few years video quality was horrible. I think this will change in the future as 1 or 2 cloud service providers will keep it all. An example of this are the 'Red Light' camera's in the USA atm. Almost every city in the usa has these camera's on the entrances to the city. This data is stored in a phoenix, az companies server and can be used by LE from what I hear on the grapevine.