They’re executing said script as best as they can, and then they’re moving on to their next role or having dinner with their families or doing other normal human being stuff that doesn’t involve posting wild theories online about why Thanos did certain things in a certain order.
In fact, when Elba has talked about the MCU (without referring to it as such) in the past, it has often been to express some frustration around the whole process.
Of course they’re putting in maximum effort in order to do a good job, but not all of them are obsessing about where things are going or what might happen to their characters.
This whole thing is a good reminder to me and assumedly to other fans that for some of the people in the MCU and in other major franchises, the role really is just a job.