I've been up close & personal with the process in Texas. I assume most other states are similar. The scantron ballots (fill in a bubble, just like in school) are by far the most secure system. The only way for electronic balloting to come close would be for the machine to print out a paper ballot that was then reviewed by the voter. This is still not as good, because most voters would not check the printed ballot very closely.
Why the transition? Nasty politics. Election officials don't like the election judges. Someone's brother-in-law is a consultant for a company. Someone's brother-in-law knows how to hack the machines. Uggh.
Biting the hand that feeds IT
