Because in many places employees can't be terminated without cause. You as a business want employees to be worth than what you pay them. If you hire someone for 50k who sits around and needs direction from a manager to do anything you are taking a huge loss.
Also as an employee if you are harassing female employees (but never too much because you know how to toe the line) you create an environment no one wants to work with and from which you can't be fired.
An employee being fired is not that difficult. You can either not list the experience on your resume or take the hit and lower you expected salary. You'll never be un-hirable just because you were previously fired.
Sorry that's to be blunt crap I work in the - to your eyes socialist Europe. and I know a fair bit about how employment law works in the UK
And its very easy to fire people for cause - what its harder to do is fire some one for spurious reasons i.e. fired so you can give your nephew the job.
This is true. The employer always takes a much greater risk to hire you than you take to work there.