Why do tiers exist again rofl

the ranks exist because riot wants a biased way to discriminate against players XD

although I know nothing of the ranked system, why are their LP so low if they are in that rank?

its the way the system works, they can only fall out of plat 5 if their MMR falls below the gold 5 level, into silver 1. at which point they would then fall into gold 1, and have horrible MMR at which point they would gain little and lose a lot per win/loss.

these players are probably playing at the gold 5 to gold 3 level.

but then again, its the same reason you dont fall out of gold 5 if you lose a few games at the very bottom.