I'm sorry. I still don't understand that. What exactly is the reason?
I would say that some of the reasons are those pesky practical ones.
The stations are now geared up for the Meteor times four days in a row, and then the Star times three days in a row. So, the station employees only have to deal with the change twice a week. If they alternate between the two trains daily, the employees will have to change every day.
For similar reasons, Amtrak knows how to turn LD trains around daily. So, the Silvers will run normally and then stop running, changing just twice a week. If they alternate, they have to change daily. That's a lot of switching back and forth. IMHO, a major part of this is that there were typically two of each Silver "in flight" at a time. For example, if you checked the pre-pandemic "where's the train", you see two 91's, two 92's, and so on, in movement at the same time.
Not that one could not redesign the system, but that would be more of a dramatic (traumatic?) change for Amtrak.