Why video cameras are ideally not required at workplaces?

There are reportedly a lot of incidents where workplaces' funds or trade secrets get revealed by someone inside the company to outsiders or competitors.

This has given rise to the usage of CCTV cameras or video cameras at many companies.

But why do you not trust 99% of your employees who are loyal to your company and won't involve in any such task that will harm your company's reputation?

Just because 1 person will do fraudulent activities, why do you not trust the rest of the lot? 

Think about this and hire only the loyal ones after cross-checking and verifying their work ethics.

You won't need to then keep these technological devices to keep a check on all of your employees.