In javascript we can prevent user from pressing various keys, that I know.
But a disabled key such as F12
can prevent user to access to developer tools or say preventing user to right click can do the same. It's a very good idea from security point of view, then why all major sites don't implement such scenario in order to protect their hard works such as various CSS and Designing.
I want a logical answer. If any reference for the sites with such implementation is needed then tell me I'll update my question with that link.