Here is the answer:
Land prices in the East were getting too expensive, and the West (the Great Plains) offered an opportunity for more people to own land. Some people suffered from extreme weather and poor soils, and many other people decided to take the risk and venture to the Great Plains. Their government was also committed to supporting those who decided to make the move.
The settlers from Europe seeking freedom saw an opportunity in the move to the Great Plains, it offered European immigrants to escape poverty in their home countries.
PARAPHRASED:
Basically, the prices weren't affordable in the east. The Great Plains was different though, it opened up opportunities for people like the Europeans immigrants wanting to escape poverty from their home countries. Although the soil was weak and the weather wasn't that good either, people still decided to take the risk.