You only tap to strikes when you're hurt and with no hope in sight, Conor has probably seen Khabib's fights thousands of times and knows how he'll behave and has prepared if it goes to the ground. It's unlikely there's be a situation with no hope, even Barboza and MJ who had it bad had multiple opportunities to see the next round. And Iaquinta fight has shown that Khabib's cardio is not that good either, and will slow down eventually.
Khabib's damage to opponents is not that good, Horcher survived longer against Khabib than Lando has against Ferguson (which was Ferguson's weakest fight and Khabib's most dominant fight)