What do you think of scooping the opponent's kicking leg and throw him off the ground?
If he kicks to the center-body and retracts you lose your balance and he gets your head. If you block a center body kick by diverting it to the side and counter attack you are in good shape. If you attack him to the center body and he tries to scoop your leg the momentum of your retraction will take him out of balance and you can grab his head.
You can scoop his leg if he kicks your head to take him out of balance, but why wait and try and figure out what he is doing and wasting time that can be used by him to be more efficient. In the kicking range, you cannot afford to assume he is doing anything but a direct center body kick because this is the most efficient. If he advanced forward you treat it as such. He would have to be a little closer to attempt kicking for your head, and it would have been easier for him to punch you in the face instead.
When its hard to judge the exact distance, when his body telling you he is about to deliver a front kick you treat it as the most efficient one anyway. If he has to move closer, you already counter attacked. In fighting sports the foot does not have a glove like the fist, so it might be easier to knock someone out with a kick the the face, and it is not permitted to kick him in the groin and let him bend finishing him with a blow to the back of his neck. So you might expect kicks to the face, but the kick could be done to the center body as well which is more efficient.
You cannot afford for him to get that close with a kick to the head. You only assume he kicks to the center-body since it is the most efficient (fastest reach). And you need to be efficient in your defense and offense, so you make your decision on time to treat every possible attack as the most efficient one.
If it was not the most efficient one, than you hit him before he even attacked. In fact you had much less to do.