Remember, for example, how the Empire bombed Mandalore for insubordination. Why didn't this happen here? That is, the entire system abandoned the Empire, simultaneously destroying a large imperial fleet, and the emperor did nothing about it.

In universe explanation is from The Rebel Files which say that Lothal continued Imperial ship production after 'liberation'. So combine that with the fact that Lothal had been pretty much strip mined for resources and you have little reason to retaliate.

Especially as there are uprisings happening elsewhere throughout the galaxy. Focus on what can give you meaningful outcomes.

But Palps is well spiteful so I agree with surprise that he didn't waste Lothal just because he was annoyed.

I was always under the impression that the events of Rogue One and A New Hope happened pretty much immediately afterwards, so the Empire simply did not have time to embark on a campaign to recapture Lothal. Also, if you were an Imperial officer, would you be the one to volunteer to attack the planet where the Grand Admiral was seemingly killed? The Emperor was no coward, but many of his servants definitely were.

Yeah, Thrawn himself believed that Lothal's destruction was inevitable, and there's no way he said that to Ezra without the Death Star in mind. The preventing factor is that the Rebel Alliance attacked Scarif immediately afterwards, so the Empire shifted to completely focus on recovering the plans and finding the rebel base. For that matter I'm pretty sure The Rebel Files is outdated as a reference source.

Palpatine assumed that Thrawn was dead and knew that Ezra destroyed the astral gateway, so he had no direct interest in Lothal anymore either. He didn't necessarily fear the rebels, but knew that if they defeated Thrawn, there was no way anyone else could take the planet, at least not easily.

Then the Death Star was destroyed and most of Imperial High Command was lost. Tagge was put in charge and focused on strengthening the Empire internally before regrouping to pursue the rebel fleet. You could consider him fearful of the rebels, but it's more like he knew it wasn't worth the effort to conquer a planet that had liberated itself and wasn't directly involved in the war thereafter. Then he was killed by Vader, who had by then learned that Luke was his son.

It just keeps getting more complicated. Nobody was even thinking of Lothal anymore at that point.

Mandalore is a different case because the Empire still did have a presence there and faced the planet in open war, but the Great Purge only happened after the second Death Star was destroyed. All bets were off.

the Grand Admiral himself was kidnapped

Lol that sentence sounds so funny for some reason. I guess because I never viewed what Ezra did as kidnapping, but I suppose it technically was. XD

The Rebels finale showed that some stormtroopers were sent, but they were suppressed by the people of Lothal who defended their own planet. I don’t know why Palpatine didn’t send more or a fleet though, however I’ve heard people say that it’s because Rogue One and A New Hope happened pretty quickly after the Rebels finale, so Palpatine’s focus was pulled to other stuff like the Death Star.

Well Palpatine probably lost faith in Thrawn after his “failure” to defeat the Rebels on Lothal. So I would say it’s because while the loss of Thrawn was disappointing to him, he did not care about that as much as he did defeating the Rebels once and for all, because the end of Rebels is when the Rebellion REALLY becomes a big threat to him and his power.

Pretty much immediately after Lothal was liberated, the GCW kicked off in full force, making the Rebel Alliance the priority.