Just imagine you have to explain a child in kindergarden how the collective choice is made. Raising hands works. Putting different pieces of paper into a jars works. Magical machine says the result was X does not work unless they trust it, regardless of how correct the magical machine was under the hood, because the majority lacks the skill of intuitively understanding this themselves. Sure, they could trust an expert or an figure of authority, but that is a fleeting thing. A fleeting thing that may be enough for inconsequencial decisions, but not enough to steer countries.

Even I as someone who would have the skillset to understand why it has to be correct would have an easier time verifying a paper ballot process than ensuring that network connected complexity behemoth was running the program I checked for weeks correctly in any moment during an election. And even if you had a way to guarantee that, who tells me this was the case in the whole country or thst evidence wasn't faked a millisecond before I checked?

Meanwhile with paper and poll watchers from each party it is very easy to find actual irregularities and potential tampering — trust is a gradual thing with paper while it is much more binary with digital. If there is a sign for the digital machine being untrustworthy you can throw the whole result into the bin.