That's because most of the criticism wasn't in the form of conspiracy theories or accusations, but instead in the form of technical or at least logical arguments against their use. It was, "this is a problem and it isn't being addressed at all."

With the 2020 election, it was -- after the fact -- "all these machines are now corrupt because I lost". And I use the term "I lost" because it was the Trump campaign and it's most adherent supporters that were making the claims. And then there were recounts and investigations... which turned up nothing, but the complaints continued into court cases... which also turned up nothing, but the complaints and court cases turned into rallies... which became riots and insurrections.

So the difference is that the first group was largely rational and reasonable -- you'll note the distinct lack of injury and death -- while the second group ignored the facts, didn't care about the actual problem of the machines, and used it as a scapegoat to fuel insurrection, violence, and populism.

I'm sorry if you can't see it, but it's really not very subtle.