You are nitpicking at this point. A runway may be clear when given the clearance to land. And that happens about 4NM from the RWY threshold. In the meantime a

You are nitpicking at this point. A runway may be clear when given the clearance to land. And that happens about 4NM from the RWY threshold. In the meantime a incursion might happen. Given low visibility you may not see it as you land a big airplane whose nose is a bit high up because of the flare. And even if you see it, it takes a few seconds for engines to spool up to full power in order to do a go-around.