Why aren't mobile surveillance units more popular?

I am wondering why mobile surveillance units are not more popular.

I recently moved to an area with an extremely high crime rate. Property and violent crimes are very common. I saw a mobile surveillance trailer at one of the local grocery stores, and it made me happy to know that one of the nearby areas had good surveillance available.

However, as I get closer to my house, the units do not exist. There have been multiple murders in the past month in nearby parks and on my street. The simple presence of these units might deter violence.

What is stopping cities with high crime rates from implementing security trailers in parks and high-crime areas? From my understanding, there are a ton of benefits and capabilities.