Software and hardware is still magnitude more vulnerable to intentional misbehavior, and even accidental mishaps has a higher risk of massive negative consequences, and its harder to discover failure compared to boxes of votes that has a physical presence.
They can see whether another candidate's ballots are piling up faster than yours, they can estimate whether a table counting ballots for a district you're expected to dominate is being given way fewer ballots to count than you'd expected...
Yes, they would obviously spot if some election worker is like adding a pile of pre-marked mass produced ballots to a pile or something, or if they were just putting half of your ballots in the wrong pile - but stuff like that basically never happens, whereas somebody will win and it'd be nice to know before it's announced if that's achievable.
And the other related issue is that in 2025, it simply should be possible to vote from your phone in a way that verifies your identity, if you'd like, using the faceId/fingerprint biometrics that most smartphones from recent years have.
Paper ballots are fine. It is not complicated at all and an election is the one thing you just cannot get wrong in a representative democracy. It can cost a bit and you only do it once every few years.
And if anyone can make up a reason to doubt the outcome of the election, it will fail it's objective: Peaceful transfer of power.
The usual way to try to solve this is the ability to override previously cast votes, in secret. But the combination of that and the ability for all interested parties to independently verify the count is not trivial. But not impossible either, much has been written on the subject since e-voting was all the rage in the 90s. One would do good to study this work before designing yet another voting system.
Sounds like externally verifiable logic systems is an upcoming need.
E.g. You as a Citizen walk around with your own System Verification toolkit and can at any time Verify that the voting system tabulates your vote. Something fantastical like that.
Trust is hard to maintain with human. Digital trust is not a human concept, the way I think at least. So this area is tricky.