Just Plat 4 so I can't really talk about "Low elo players", but especially Iron - Higher Gold doesn't quite understand that there is different phases in League.
Sure they'll go "Oh we win late game, we got tankyness or lots of damage". But they don't REALLY get it.
Kayle powerspikes, as Krynn put it, on level 11 with 2 Items. That's when she can gain momentum quickly.
It's sort of like giving your enemy a head start and if they don't get a good lead in that timespan, you catch up to them devastatingly quick.
Especially low elo has a short temper as well. They die as kayle? "Well, gotta equal it out, kill the enemy to get even."
They do that 2 or 3 times and then it's over. The enemy will towerdive that Kayle with ease (if she doesn't have R).
After the spike however, Kayle becomes a powerhouse.
The short temper also resonates on botside btw.
Some people can't accept losing the lane early. They start tilting and run it down. Sometimes it's better to accept that you died and play cautiously and focus on your gold income through farms (and perhaps camps) instead, to avoid getting kicked out of the game by your enemy.