I can only imagine they didn't have much confidence from his 30 game stint in 2022-23. They traded for Sean Durzi to fill the role that Soderstrom would have competed for. They signed Matt Dumba to eat minutes and kill penalties, the latter wasn't likely something they envisioned for Soderstrom. Soderstrom was drafted by the previous GM, so the current administration isn't as married to him.
Looks like most of Soderstrom's 30 games in 2022-23 came in February-April when they were finishing the stretch. Gostisbehere and Chychrun were traded at the deadline (for draft picks) on March 1st. So this might have just been a case of calling up a player because they just needed a warm body versus being called up for merit.
Your assumptions aren't completely false. They did sign Dumba late in free agency and the way he played most nights, he looked like he was expected to be traded. I speculate he was signed to gain draft capital.
The season before they did call up Soderstrom to see how he would react and allow Chychrun to sit before the trade deadline and avoid getting another injury at the wrong time.
And then there was the time before, when he ended up in covid jail right after a call up and screwed up his season.
Some bad luck, some joining a weak blue line and not standing out, and then being replaced by Kesselring on the depth chart.
