Fabi wasn't looking for counterplay, he was looking to secure his king. If he managed to do so in a few moves, he would have less to lose by playing on than Mag

Fabi wasn't looking for counterplay, he was looking to secure his king. If he managed to do so in a few moves, he would have less to lose by playing on than Magnus. Giving Fabi a chance to fend off Magnus' attack only increases the chance that Fabi plays on.