There are multiple reasons why they may have come to the US. Following Napoleon's defeat in 1815, Germany, which was still divided into various kingdoms, was trying to recover economically.
1. In the 1820's the German population was growing and there weren't enough jobs or opportunities for people. Since there weren't jobs many left and went to the US.
2. For those who grew up on a farm, which was most people, the oldest son inherited the farm and the others had to find work elsewhere. I wonder if Valentine was the oldest who then inherited the farm and the other two brothers emigrated.
3. The prices for grain and other crops dropped so there was little profit for those who were farming. Most farmers in Germany were beholden to nobility and had to deliver either 10% of their crops and animals or had to deliver specified amounts of grain, animals, etc. to the nobility who controlled the land. With poor harvests and low prices it made farming so much more difficult. Because farmers suffered under the burdens of the nobility they began to demonstrate and fight for their rights and have the burdens removed. Since my ancestors lived in the Kingdom of Hanover, those burdens were only lifted in 1831. In the US there were no nobility, people had the right to vote, one owned the land and you were not bound by the many burdens and rules in various German kingdoms and you were free.
In many Germany villages and towns there often were mass migrations to the US. For example in my ancestors village in Lower Saxony with a population of 1,000 there were 500 people who left between 1835-1850.
Hope this helps. Ron Wedekind