I guess it was "better safe than sorry". Considering what they had been trying with Klishina, I can understand that. And Russia is good enough to win Olympics anyway. I wonder, has any team ever defended their Olympics title?
EDIT: I checked, and yes, Soviet Union and USA once did.
why ? American volley Maxwell Holt had a meldonium case yet if Markin gets banned he should have been too, his case would have been overturned anyways by CAS like Efimova or Klishina, anyways I guess it was more psychological, if he had to appeal then the team would have been stuck training thinking in their heads if they will even compete or will be a distraction psychologically.