The difficulty can only drop 75% or less and it can only raise 300% or less every 2016 blocks. Source

Shitcoin forks often reach these maximums because their miners are not loyal and will switch to more profitable forks.

During these periods, those chains may have 2+ hr blocktimes for many weeks or 2 minute blocktimes for a couple days. Its inconvenient/convenient, but it hasn't "killed" any of these forks so far.