From a technical standpoint, why don't more websites include 3D objects?

I've been learning JavaScript and the 3D-object manipulation library called THREE.js. It's relatively simple to use, set up, and get things going. This has left me wondering- why don't more websites include 3D-objects?

Especially retail websites where the user can play with the 3D version of a product they're considering purchasing; whether that's furniture, a car, etc.

My amateur guess is that performance would take a hit, but my own page seems to run fine.