Question

Why are more and more people shifting to other sectors from primary sector

Answer 1

First you need to understand the concept of  stage of growth .
India has its uniqueness if we compare stage of growth with other industrialized countries of world. By the end of  19th century  it was well established fact that industrial activities are faster way to earn more income in comparison to agrarian activities. As countries after countries successfully industrialized, a pattern of population shift from one to another sector established, Which is known as Stage of growth.

India is an exception for this concept  as its secondary secondary sector didn't grown as it should be

Reasons :

Post independence public sector oriented Economy policy  : As during the first 45 years after independence, India’s economy was divided into two distinct segments, private and public. The private sector owned and operated small to medium size businesses and industries protected by the government and the government took care of everything else. The intention of the government was to provide these services, at a reasonable cost, as well as employment.India’s economy and political system encountered a severe crisis during the time of Indira Gandhi and her Congress Party rule. During her administration, there was no economic progress because of a lack of attention to economic improvement. Absence of capital goods industry to promote industrialization.the red tape, bureaucracy and the Licence Raj that had strangled private enterprise. Absence of infrastructure.
Absence of market for industrialized goods as large chunk of population was poor.Fear of foreign domination due to colonial exploitation led to socialist approach.Now how sudden shift to tertiary sector ?

In India , the share of agriculture in GDP was more then 50 cent- as we would expect for a poor country, but by end of 1990 the share of service sector was 40 cent more than that of agri or industry like we find in developed country. The recent emergence of a dynamic service-led Indian economy thus has long historical roots.
There has been a longstanding bias in educational investment towards secondary and higher education, which has produced a small group of highly educated workers, who have worked largely in services.
LPG (Liberalization privatization globalization ) timing of Indian economy was well synced with IT industry boom. (transformed to Knowledge based economy)  The growth in the IT sector is attributed to increased specialization, and an availability of a large pool of low cost, highly skilled, educated and fluent English-speaking workers, on the supply side, matched on the demand side by increased demand from foreign consumers interested in India's service exports, or those looking to outsource their operations.During the Internet bubble that led up to 2000, heavy investments in undersea fibre-optic cables linked Asia with the rest of the world. The fall that followed the economic boom resulted in the auction of cheap fiber optic cables at one-tenth of their original price. This development resulted in widely available low-cost communications infrastructure. All of these investments and events, not to mention a swell of available talent, resulted in India becoming almost overnight the centre for outsourcing of Business process.