Which is why e.g. Germany does all elections solely on paper, and still has early results just an hour after the polls close and final results the next morning.
Making semi secure software that tallies digits somewhat correctly for the 90% of the time. And its mostly good enogh.
But for important things like elections, making software secure and robust enough is a lot harder (and trusting that it was done so even more) than just using paper.
Same way most of us are still wiping our ass with paper, even though there are some more technologically advanced toilets that probably clean you better.
It's such a bad idea that Tom Scott has not one, but two videos on it:
https://www.youtube.com/watch?v=w3_0x6oaDmI (Computerphile channel)
https://www.youtube.com/watch?v=LkH2r-sNjQs (his channel, more recent)
And also, if 20 people can handle ballots from 1000 people (no clue if that's realistic but it doesn't matter), then if you add another 1000 people.
Well... since you added people and the resource you need to count is people it's a self scaling solution. Sure you might need larger facilities, but we're not exactly running out of schools (another thing tied to the population).
The only reasons to make voting electronic are:
* To make money
* To commit election fraud
which is why I said there are no "good" reasons. :)