Why do they still keep away from American culture?

As told by Albrecht Powell "The Amish are adverse to any technology, which they feel weakens the family structure. The conveniences that the rest of us take for granted such as electricity, television, automobiles, telephones and tractors are considered a temptation that could cause vanity, create inequality, or lead the Amish away from their close-knit community and, as such, are not encouraged or accepted in most orders."

For example, they cultivate their fields with horse-drawn machinery instead of things like tractors or other electrical machinery.

The fact that the Amish are already using technology for certain things helps prove my point even more that eventually the Amish will have to advance their use of technology.
http://pittsburgh.about.com/cs/pennsylvania/a/amish_2.htm