Slowing Down Next to 18 Wheelers

Genuine question: Houston, or people in general, why do y'all slow down when you're coming up on an 18 wheeler that's in the OTHER lane?!

I mean, IF you're so nervous or scared of being next to one, wouldn't you speed up so you can hurry and get past it? Some of y'all are literally sitting in their blind spot. Like wtf? 😅

Otherwise, please make it make sense please. I'd like to know if I'm missing something.

It also clogs up traffic around that truck. Get tf outta here with that. It's dangerous!