Eligibility to vote is still determined by officials looking in large books of registered voters delivered from the local board of elections. The results have to be transmitted manually to a central tabulating center and only then released to the news media. The answer is simple. Just as competitive capitalism forces innovation, so monopoly discourages it. And government is the largest monopoly of all.
Most boards of election are perfectly happy with the status quo.
Even when some new technology has crept in, it is a half-way measure at best. In some jurisdictions, computerized voting machines have replaced the old mechanical ones, but that is all they have done. The ladies with the great books are still there, looking up every voter. The results are still officially delivered by hand to the various boards of election. The votes would be transmitted instantly to the central computer and at the close of polling, results would be instantly known.