Mark and Haechan are still running in parallel with the schedule between NCT 127 and NCT Dream until they are tired but still completely come to the end

Why did SM let these two guys work to the point of exhaustion because of the overlapping schedules of the two groups?

I see that Haechan and Mark working with NCT 127 still have a completely different concept from Dream, so when the two of them come back to work with NCT Dream, I see that they are different from all other members of NCT Dream.