Why isn't there a common voting system?

edition.cnn.com

I think that the fact that electric voting systems are different between states will cause serious problems.
The first one is that difficulty to vote online would cause different voting rate between states.
The second one is that some states can have just poor security systems, due to lack of human resources or money. There may be criminals who try to vote multiple times or delete a candidate's ballots.
So, US government should prepare a common platform for the electric voting system.