Rags were desperate to give him up. Why even offer anything? You can just sign a veteran dman in the offseason for some leadership that won't cost you $8.5 million. It's not like they're going anywhere this year so they don't need it that bad.
And if the rags turn down your offer of just the contract to go back the other way? Oh no...
Also can just take him for free on waivers.
Just playing devil's advocate for Anaheim:
Vaakanainen was a smaller cap dump the other way. Taking Trouba for "free" on waivers would have meant the Ducks were also on the hook for the remainder (1.1 mil) of Vaakanainen's contract. As much as we like to think every owner is a bottomless cash dispenser, Anaheim's typically a budget team.
Verbeek probably isn't on the hot seat, but I wouldn't be shocked if he/Anaheim's ownership is disappointed with how they're doing this season. Ignoring the cap hit, Trouba will definitely balance out their D pairings. Not sure if Verbeek has enough of a leash to tell the owner "Welp, this season's lost. We'll make some changes in July."
Anaheim's typically not a hot spot for UFA especially as they're rebuilding. They had to overpay Gudas/Killorn recently. The RHD crop of UFAs this season isn't great: Aaron Ekblad, Neal Pionk, Jeff Petry, Cody Ceci, David Savard, 40 year old Brent Burns.
Trouba's contract was frontloaded so he's "only" making 6 mil this year and next while counting 8 mil against the cap. That's the sort of contract Anaheim has liked in the past for budgetary reasons. Trouba can keep them over the floor as they look to trade Cam Fowler and John Gibson.
Trouba's not blocking anybody in their system, if anything he buys time for Tristan Luneau to get some AHL seasoning. And if Anaheim is a seller at the 2026 deadline, a retained Trouba should fetch a lot more than the 4th round pick that they gave up.
Anaheim wasn't the only team trying to trade for Trouba. We know that Trouba said no to Columbus, but we don't know if there were other teams. Anaheim would have had high waiver priority but didn't want to risk Chicago or San Jose from making a claim. Anaheim has had a bunch of picks in recent years and in the future, so a 4th isn't going to make a huge dent. They can probably get at least a 4th round pick for Brian Dumoulin at this year's deadline.