By after release it's days after. So at that point they were probably focusing on DLC for SV, Z-A probably ramping up further, and Gen 10 getting into the swing of things..
So instead I want to offer the following alternative theories:
1. They booted up the older builds for these screenshots because they were going to reference them in future talks. They didn't use these ones specifically, but they wanted them on hand in case they did.
2. They brought back this build specifically for reference in Z-A, a game we have still not seen in action. They might have wanted to reference either the performance with the lighting engine or textures, or the colors to go for, or just "could we aim for something like this in this type of game instead"
3. The same as 2, but for a reference point for Gen 10 specifically. It clearly didn't pan out for SV, either because of their own issues or the Switch or both (probably more the former though....), but Gen 10 can potentially use Switch 2 or, at least, make use of any extra they learned over the course of developing SV & Z-A. Or just as simple as "hey let's add this to our moodboard".