There are likely non-Americans (and Americans) reading these comments who might not know a lot about Carter. Here are some thoughts on him, for those who are unfamiliar.
I used to produce a regional television show in which I traveled to various cities in Georgia and Alabama to shoot fluff segments.
Carter still taught Sunday school at a church in Plains, GA. He ate lunch at a peanut novelty shop/restaurant in town once a week. We had lunch there and I interviewed him, along with the shop owner. I don't remember about what specifically, probably peanuts. Not much else to say about Plains. Carter and peanuts. That sums it up. (I kid. I kid.)
He presents as a grandfatherly, innocuous Boy Scout, and maybe because of that, people forget he's a genius. Not in an ironic, "Oh, look the hillbilly can count to 10" way, but genuinely, by any measure, brilliant. He has a grad degree in nuclear physics and graduated near the top of his class at the Naval Academy. IIRC, I read once that his IQ is estimated in the 150s.
It's sometimes pointed out that his peanut farm business failed, but there's more to that story. To avoid a conflict of interest, he handed over management of the farm while he was in office. It was mismanaged while he was away and put him in debt.
One of Carter's problems was he wasn't good on camera. His accent makes Bill Clinton sound like a Bears fan. And he has a slow, almost droning, speech pattern.
His presidency was at at time when, more than ever and increasingly so, people wanted snappy, simple answers to complex questions. Carter had a tendency toward complex answers that were anything but snappy.
We wanted flash! A little pizzaz! Carter is wholly sans pizzaz; something we can appreciate in the age of Donald Trump, but at the time bored the shit out of us.
The presidents who came after him were camera-ready. They spoke quickly, more definitively and said what we wanted to hear. Carter was arguably too frank and way too honest. He said what he thought Americans needed to hear to solve our problems, not what would get him reelected (a lesson in what not to do for all future presidents, lol).
His Crisis of Confidence speech sounded like your dad nagging about the importance of car maintenance. Sure, later when the car broke down, we realized dad was right, but at the time, we just wanted him to stop riding us. He was certainly no dreamy cowboy with fabulous hair promising a Delorean in every driveway.
Carter just wasn't suited for D.C. Soon as he got there, he set about pissing off both sides.
First day in office, BAM! Pardoned all the draft dodgers (<cough> Ahem, Jim, that's something you do on your way out of office . . . ). Before the week was out, he started in on pork barrel spending and never shut up about it. He threatened to cut all of it.
Many presidents proclaim to be religious. Carter actually is. Whether that comes as a relief or scares the hell out of you, the point is, it's not typical.
Even today, he openly supports Palestine, for fuck's sake. Lol.
Bottom line, he shined a big fat light on a lot of D.C. hypocrisy. Folks don't like that.
He made mistakes. I'm not even talking about the whole Iran hostage thing.
Mostly amateur and/or idealist stuff. For instance, he brought his own people into the White House. He was praised for this by the public initially, but the reality was they were unprepared and under-experienced for the big leagues. They may have been loyal and hard-working, but running peanut plantation or even the GA governor's office is not the same thing as running a country.
I think when Carter was elected, both sides thought they could control him. When it sunk in that he was a rocket scientist merely disguised as a yokel (some say deliberately), they got rid of him. His own political party fucked him over on his health care policy.
It could be argued he did more good since leaving office.
Carter is inarguably a man of principle. The only question is whether or not you agree with his principles.
Of course, this is all just my two cents. Here's his Wiki page.
He's been on the right side (IMO) of many tough issues, even extremely unpopular ones (he's always heavily favored policies of racial tolerance; he's supported decriminalizing of cannabis since the 70s; he publicly criticized Obama for not closing Gitmo, etc).
You may not agree with all his policies, but there is so much more to this man than his "aww shucks!" persona.
Disclaimer: I'm too lazy to check my work. Sorry, but it's late. If I made a mistake, kindly correct it. Any mistakes are due to stupid late-night brain and being an old, forgetful woman and not a diabolical plan to mislead anyone. I didn't read the Wiki article, but I didn't say anything revolutionary; I'm sure everything in my comment is sourced there.