Why people might go for this:
Parson- Assuming the Archons fight hard enough to win up there, and it looks like they are winning, Jetstone's fate is up to Parson. He could call the Archons off and let the Jetstone Healomancer through to Trammenis. Whoever's left in charge of Jetstone has nothing to lose by allowing Trammenis healed, it's do or die since he croaks next turn anyway. For Parson, it's either show mercy or behead the entire Jetstone side, being responsible for thousands of disbanded units. Parson wouldn't want to destroy the side if he can help it, he still feels bad for all the lives he's taken so far, and it's wasteful. He may not know that much about Trammenis, but if he asks around he seems like a reasonable enough Diplomat. Nothing to lose. If Trammenis tries something they still have a lot of ground and air units. Probably.
Trammenis- His situation is assumed to still be precarious. Archons above, Silvia's forces in the keep, his odds of escaping aren't good. Diplomacy is his strong suit anyway. He may not like Decryption, but it would allow his father to live again and even be King again. It would also prevent the disbandment of thousands of his citizens. Parleying with Lord Hamster instead of attempting a near-suicidal escape means he gets to have that conversation with Parson he wanted anyway. Lord Hamster has proven himself to be just as tactical as Charlie said... and thus just as useful against Charlie as estimated.
Stanley the Tool- How often do you get to have a King bow down as _one of the Units you control as Overlord_?? Even Stanley couldn't resist that, a King being subordinate to a Tool. At first, missing a chance to raze an entire side's city seems infuriating, true. But Gobwin Knob is already pointlessly rich from all its gems, it doesn't need more cash. Especially since Charlie has quietly cut off the Gobwins as natural allies, the schmucker dump for cash. What Gowbin Gnob needs now is a more allies and a way to beat its City Cap diminishing returns. Having a Pocket Kingdom that is technically its own side accomplishes that. Instantly double your production without doubling your diminishing returns. Gobwin Knob's schmuckers reserve is just what the cash-strapped Jetstone needs to keep rolling out all its otherwise good production line-cloth siege, heavies and infantry units, it's really a good hybridization. Charlie would go nuts.
Wanda- Controlling Jetstone means she further cements Ansom's loyalties back to her... and away from Jillian. Ansom has twice the reasons never to turn when his two loyalties merge- Jetstone his home country, and Wanda as his pathway to the Titan's will for Erfworld. And, Wanda can use her Attuned Influence to order King Slately against designating another heir and splintering. Although she could also order him to splinter off and be Loyal to her still too. That's a mighty useful puppet to have.
King Slately- He gets to feel like he finally owned up to the Duty he was shirking as a King. For too long he held court and risked everyone but himself. The same day he was willing to give his life for Jetstone, is the same day the Titans and their Tools allowed him, and his entire Side, live again. He proved he was willing to croak for what he believed in, and for this the Titans gave him a second chance. To betray the rising force of the Titans would be to turn against everything he lived, and died for.
Archons- Decrypted Archons do what they're told!!! They don't need a reason.