Who says they didn't?
I sometimes feel like the sheer volume of things fans demand be explicitly explained to them would utterly ruin a show and its pacing. Do we really need to know the details of these things, given that they don't push the narrative forward at all? Can't we just accept the story as they chose to tell it without being spoon-fed every background detail?
I was just saying that within universe what happened to those crews is the bigger question than "where's Soji?"
But I guess now that you bring it up, I disagree, and this has nothing to do with me needing to be "spoon-fed every background detail". I think characters should be written with consistent believable behavior. It's one thing to have inconsistent character motivations when you are trying to corral the characters together to tell a particular story in the context of an episode in a series where episodes are expected to each tell mostly self-contained stories in a rigid time frame (ie: pre-streaming Trek). I've done enough writing to know that it's hard to make characters do what you want them to, and I'll forgive some inconsistencies when writers are working within tight constraints.
It is quite another thing to be inconsistent in the context of a show in this era, where they have a whole season to tell a story (in episodes that themselves it seems can vary by about 10 minutes in length), to needlessly make two of the characters somewhat implausibly reinstated as starship captains (Starfleet is full of great officers, I don't think they need to reactivate retired ones with checkered pasts) and then have them drop their responsibilities to their crews (which Trek has trained us to know that starship captains put the highest priority on) as soon as that element of their characters was inconvenient to the story they wanted to tell. They had a timeskip in part to give them lot of leeway to put the characters wherever they wanted to set up the season, so I'm going to hold them to a standard of positioning them for the story they want to tell.
I can maybe buy that Rios would just quietly decide to himself that the best thing he could do for his crew was get with the time travel plan, or make whatever attempts he made to contact them without ever mentioning it to anyone else. That seems reasonably consistent with his character. But I really don't don't buy that Raffi would have a lost crew and constrain her efforts to help them to going along with the plan, which she is otherwise pretty vocal about not liking, or that she would otherwise stay mum about the issue. Not that I need more complaining from Raffi, which is what I suspect acknowleging that the crew of her ship is lost in fascist future would consist of. But the solution, if they didn't want to explore this aspect of the character, was to not needlessly put her in a command position when they could have easily worked her into the story in myriad other ways.