Your employer writes the contract and they write it specifically to remove as many rights from you as possible.

Thats the definition of employment you sacrifice your freedom for money so you can buy food and a roof over your head.

In the UK if a contract infringes on your rights then the contract as a whole is void but most employers will still write up illegal contracts to pressure their employees. Most employees don't know what their rights are and if they do they don't know that legally they can't sign away their rights so the contract doesn't matter, but even if the employee knew all their rights its cheaper and easier to get a new job than fight it in court.

In other countries like the US you can sign away your rights apparently Canada is the same, this is metal to me that some one could legal sign them selves into slavery in the USA and Canada and no one has a problem with that?