Why does Learning English Language is compulsory to get a Job?

It depends. If you are living in an English-speaking country, it would be a completely normal job requirement that you speak the language of the country. How else would people be able to communicate with you? It might also lead to serious work and health hazards if you could not fully understand a job's safety requirements that are posted on machinery or elsewhere on your work site.

Even if you live and work for instance in a Hispanic neighbourhood in the USA, knowing English will be essential to communicate with customers and other third parties you may come in contact with. And it may well hold you back for promotion.