This answer in a nutshell: Money
Let's say the time period you're talking about is the California Gold Rush of 1849. Factory workers in 1849 could get paid $1 for a 12-hour shift in the United States (around $39 today). Being a good miner of gold in California could get you around $30 (around $1,157) a day. Many men wanted to strike it rich and leave their homes to get all this money.
This could be relevant in any time period, but the values could change. However, in most time periods, many men still wanted to get a lot of money from gold for their families.