The problem with the block chain is privacy. Publishing people’s votes can and will have a huge impact on their life. It would also make buying votes much easier.
A block chain solution would have to find a way to ensure that only valid voters can place a vote, ensure that only people that could vote were the only people that placed a vote after the fact, and ensure that none of this can be tied to a real identity. Otherwise, either bad actors could place votes, or a complete voting record for a person is published.
Solve all of the above, and a block chain may be an acceptable way to go, though it would be a waste of energy in my mind compared to a normal database, which could easily be exported with only the vote and signature stating it was a valid and verified vote for a person.
In the end, we have just made something more complicated than a paper ballot, which has been shown to be reasonably secure against foreign and/or national actors attempting to influence an election, except in already corrupt nations, especially those without term limits...