As Dominique Ducharme mentioned this morning, it's not a question of effort or attitude for Romanov. We can deduce that it is not to punish him, but rather to create a certain spark.
Alexander Romanov is a pure worker, let's emphasize. He is almost always one of the first players on the ice at practice and one of the last to leave. That's what Romanov did this morning, he was the first one on the ice to tell Dom Ducharme that he was ready to come back into the lineup. However, with yesterday's good collective game, it would be surprising if there were any changes on defense for the next game.
Romanov, 21, absolutely needs to get some ice time to develop his hockey skills. He won't find his game consistently by being left out.