I think that's mostly as opposed to, say, tree-dwelling spiders... but then again, you know about ballooning, right?

https://en.wikipedia.org/wiki/Ballooning_(spider)

Key quote: "Even atmospheric samples collected from balloons at five kilometres altitude and ships mid-ocean have reported spider landings."

Holy shit. Someone needs to do something! These little critters sneaked into that position with no one noticing. They are definitely up to something! Think about the children!!!