The reason: The new electronic voting machines, the results of which have not yet been subject to significant legal tests. (nystateofpolitics.com)
Doing so will significantly diminish the likelihood of electoral fraud, which is a huge issue despite the prevalence of electronic voting systems. (entrepreneur.com)
No one has yet come up with electronic voting system that 99 % of people can understand how it works in enough details to personally know it is secure. (politics.stackexchange.com)