I think the OP is a very valid question. It's not a matter of it's only a Beta and stuff will be added, it's more like. at some point in development atmospheric scattering was there and in more recent material it's gone. It could be the beta builds used for the latest batch of screenshots had it disabled. or they had to make the decision to remove it. I find strange that for EA sales they are not showing the best their engine can deliver at the moment, so I'm inclined to think that raleigh scatter and other features like rocks on planets have been tuned down or removed for performance. We will see in a few weeks. If KSP2 is as easy to mod as they say (I'm sure it will be the case, but still not so sure about graphic/engine related mods) then the amazing modding comunity will take over and bring it to 2023 standards like they have done with KSP1 (Thanks everyone involved in those mods, btw!!!)
https://www.youtube.com/watch?v=Ci7-5SsstFs