There are 2 main reasons for this:
- Demand and Supply
- Cost of living
The first thing is there are few job vacancies and more people eligible for that job. This gives the industry leverage to hire people at less salary. Because a lot of people would rather work for less salary than stay jobless.
The second reason is the cost of living. The cost of living in India is less than in western developed countries. You can not expect to work here and get the salary of that country. The countries with a higher cost of living pay more but when you compare the salary in those countries and the salary in India keeping in mind the cost of living, you'd realize that there is not much difference.