The key metric in the credibility of an electoral system is what is the maximum amount of fraud that can be committed with a small number of people. The paper ballot system is a remarkable piece of engineering when you stop and think about it: you have to be physically present to vote and the physical ballot is accounted for at all times, making ballot stuffing difficult to pull off on a large scale by a small number of people. The observation and counting of votes is distributed, likewise limiting the scope of an fraud.
In any electronic system, the vote moves through countless devices that could be corrupted internally or externally. Any attempt to identify fraud using statistical deviation from polling numbers now trusts the pollsters (whose numbers were wildly skewed in the final days of the last election) as much as the actual vote.
In any centralized counting system, is going to be IT team that the nation has to have absolute trust in: their intregrity, their flawless execution and their ability to detect any tampering.
Note that tampering not only covers changing the results and ballot stuffing, but also removing the veil of annonymity. In an increasingly polarized environment, being flagged in party's database as an enemy voter could easily come to affect how your career prospects in government and how you are treated by a beaurocracy
Finally, its not enough that the election is not tampered with, it needs to be provably tamper-free. It's not enough for the chief electoral officer to be satisfied with the results, the public needs to be confident that for systematic tampering to have occurred that it required a conspiracy too large to realisticly remain secret.