What's preventing you from at least entertaining the possibility that they have a legitimate grievance?
Not only do I not believe they have a legitimate grievance, I also do not believe that THEY believe they have a legitimate grievance. Ordinary Republican supporters, poll-watchers, and even some of the Representatives believe they do, but not Trump, Giuliani, Ellis, or the rest of the driving personalities behind this effort.
The reason for the former is simply lack of evidence that is demonstrable or non-circumstantial. They have reams and reams of affidavits and statements, which amount to little more than claims from partisan speakers with little understanding of the process. Nothing actually solid, nothing to show. Claims and statements are a dime a dozen. There's a reason they've stripped actual claims of fraud from the lawsuits: they don't want to have to meet the bar of proof required.
The reason for the latter is twofold: firstly, the relief they're seeking. If they were concerned about disenfranchisement, they would not be seeking the relief of hundreds of thousands of ballots from valid, eligible voters being tossed out. If Sidney Powell was concerned about disenfranchisement, she would not have requested that states simply disregard the voting process altogether and simply select their electors for Trump, voters-be-damned.
And the second reason is the fundraising effort, which purports to pay for the Trump team's legal fees and fund "recounts", but actually just funnels money towards paying off Trump's own campaign debt. This has convinced me its straightforwardly a scam aimed at his own supporters, to get him out of debt.
So, ordinary voters believe there's a legitimate grievance, because that's the impression they've been given by a public figure they trust. And that public figure is using it to wring money from them in a cynical money-grubbing scam. That's the kind of man he is; he respects his own supporters least of all.