A $40 tripod can be equated with a $500 car. YES, it's a car, buuuut....
Lightweight tripods that are small and have multi-section legs with cheap locks....hmmm...well, they move around in the wind or breeze, tend to tip over quite easily, cannot hold heavy camera/lens setups reliably, safely, or sturdily. Tend to not go very high, or very low. Often have fixed, non-interchangeable heads, and may or may not allow the use of quick release plates.
$40 TRIPODS, HMMM..... Maybe they're more like $19 jeans, versus $249 jeans...yeah, sure, they're both "pants"...or maybe they're more like $10-a-case generic beer...I dunno....$40 TRIPODS are "cheap" tripods. If all a person needs is three legs and a platform to hold a small camera up for the occasional selfie, then they're okay.