Except that the benefit is not yours, but your employer's. Let's take a look at the frontend landscape where every framework lasts 2-3 years at most. By the time you master something, you can start it over. And most employer does not support learning on the job. So you have to learn it in your spare time. The benefit is the employer's, the cost is yours. I can understand when people say f*ck it and they simply protest by not playing by their employers' rules. If they get the salary without investing time, they also reap some benefit at least.