So the Night King has spears to kill dragons but not the crew of brawn marooned on an island in the middle of a frozen lake?
The logic of these writers doesn't run very deep does it?
Some people are speculating the Night King is an iceseer and laid a trap for dragons. We know he does have abilities like Bloodraven/Bran, since he interacted with Bran in a vision to mark him and disrupted his ravens in an earlier episode. Does that mean he has similar visions as greenseers and fireseers like Bran and R'hollr followers? Someone pointed out his lieutenants brought only three dragon spears, and it would be weird to have a lone Walker off on his own with just a small band of wights, one of which isn't his and therefore wouldn't disintegrate if the Walker is killed.
So as the theory goes, the Night King somehow knew Dany had 3 dragons and would bring them all to aid Jon's suicide squad, so he sent a sacrificial Walker out to lure them into a trap and was fine keeping them alive for so long as dragon bait so at least one of the dragons would land. Three spears suggests he wanted all three dragons, in which case attacking Viserion first instead of the landed Drogon also makes sense as he could (and almost
did) take down at least two before they fled like Rhaegal did once Viserion went down.
Not attacking with ranged weapons doesn't really bother me as I don't think the Walkers/wights have ever been shown on the TV show to use ranged weapons prior to the dragon spears; Ser Royce was killed by a Walker in sword combat, the Fist of the First Men didn't have ranged combat I can remember, and Hardhome was entirely an up close melee without wights using any ranged weapons.
I'm not sure I entirely buy this 'trap' theory, though, since the wights showed no sign of stopping their charge until the ice broke.