That's a question I have, but when I Google it — to see if others are asking this question — what I get is:
Why would Trump skip the debates?! These articles were, it seems, mostly prompted by Trump's own statements — statements about the chosen dates (conflicting with football games). But it seems to me that Hillary is the one with the motivation to skip the debates. She's the one who's been avoiding exposure to challenging questions from the press by holding no press conferences. She did allow questions from the National Association of Black and Hispanic Journalists, presumably an unusually friendly group, and that event yielded up her "short-circuited" remark that's dogged her ever since.
If Hillary can maintain her lead in the polls, why would she want to subject herself to the kind of treatment we've seen Trump deliver in debates? He's been free-wheeling and brutal, even when he was fighting for the nomination and still had everything at stake. If she's on a clear path to victory, what would he do to her when he's got nothing left to lose? She might think that just standing there solidly allowing him to be offensive in her presence would make a powerful implicit argument in her favor — a reprise of the old Lazio debate. But it's still risky. There are now attacks on her physical and neurological fitness, and any flubbing of lines or seeming shakiness will be used against her.
How could she bow out? Don't the American people expect a debate — demand a debate — from our presidential candidates? Won't an attempt to avoid the debate be used against her as more of evidence/"evidence" of her physical and neurological unfitness?
She would have to handle the bowing out carefully. Get proxies to float the idea. Smoke out the arguments against it, see who picks up the idea and expands upon it. Choose some things Trump says and act like these things are the last straw making it inappropriate for her to stand beside him on the stage. He's the one that essentially forfeited the debate. And so on.
Whatever hits she may take for bowing out, they're a known risk, and they pale in comparison to the unknowns of the debate. She might make blunders. She might falter in her stamina. Trump may get off some brilliant hits that leave her reeling. Her verbose, flat, evasive style of speech might seem especially awful next to the pithy, entertaining Trump. His presence on the stage with her may catapult him into a newly presidential appearance. And how can she prepare? He likes to surprise. He might take any number of approaches, while she has only her usual, boring presentation. People may think: Is that what we want to look at and listen to for the next 4 years? Why give Trump that opening?