They are two sides of the same coin, but the law in some countries recognises that the employer has more power, and so favours the worker and makes it harder for the employer to terminate an employee without making it harder for the employee to quit.

Making it harder to fire someone makes it harder to hire them in the first place. This hurts everyone because it reduces the number of available positions by increasing the cost of hiring. Give too much power to the employees and you wind up with corrupt unions that effectively have a cartel over entire areas of the economy. It’s just layers of red tape and misery for everyone. Getting fired isn’ta problem if you can easily get a new job. It becomes a problem when nobody wants to hire because they can never get rid of you or they have to deal with a crooked union. Having high barriers to firing people also makes the fact that you got fired a giant stain on your resume instead of a fairly normal occurrence that could be due to a no fault reason.

Such systems are sensitive to multiple variable, and it's not true that all values except from the current ones lead to a worse result, or, at least, we have no reason to believe that's true. What we do know is that over the past several decades the US, and other Western countries, and especially in the past two, have conducted a massive redistribution of wealth away from workers.