What is the reason why people immigrated to Jamestown?

The establishment of the Jamestown settlement was motivated primarily by economic factors. The early seventeenth century was a period of rapid imperial expansion by European powers, and the English were in the process of building what would become the world's largest empire. America was ripe for settlement and economic exploitation, and the English believed there were significant gold and silver deposits there.
King James was only too happy to grant a charter to the Virginia Company to establish colonies, as England's economy was struggling at the time and it was thought that large-scale emigration would take some pressure off the nation's public finances. As this was a private sector venture, there appeared very little risk for the government. It was a win-win situation.
Many people were struggling in England at the time. Poverty was widespread, particularly in the countryside, so the chance to emigrate to a new land full of potential wealth and opportunity was too good to turn down. Initially, however, times were hard for the new settlers. A shockingly high percentage of them died of starvation or disease. None of their business ventures turned a profit until tobacco began to be harvested. Although it took many years for the Jamestown settlement to turn into a successful venture, the faith of the initial settlers would eventually be repaid.
https://www.history.com/topics/colonial-america/jamestown