Yoga originated as meditative practice in Hinduism with some spiritual goals that are a bit more than just the more generic “mindfulness” you might find in your typical modern fitness class.

(It’s also found in Buddhism and Jainism,)

The physical stretches and poses are great for healthy, low intensity exercise; and meditation is a thing that exists basically in every religious flavor you’d like; so it’s certainly possible to make even a “fundie-approved” version, but eh. Good luck with that.

Ultimately it could have been lumped into “other beliefs”,

It's legitimately a religion, the other organized religions don't like these ancient forms of religion that don't require payments to participate in, and can be learned for free. It really cuts into their business model.

Don't try to understand the mind of a fundie christian.

I've heard sermons that claimed "psychology" was a religion. Their problem with yoga is similar. (It has connections to hinduism. At least that's part of it.)

A lot of megachurches have classes/programs that are almost exactly yoga, but by a different name. The name they give it escapes me.

Hell. There are shops on Amazon that sell yoga stuff (mats, balls, shorts, whatever) without calling it "yoga" balls or "yoga" mats so christians don't feel sinful buying it.

And yes, they're just retailers buying yoga gear wholesale (or drop-ship or whatever) and listing it without using the word "yoga."

Edit: Googling to find if there's a common name for the christian version of yoga, I found this god-awful thing.

The term “yoga” in Hindu practice refers to a lot more than just the physical exercises. The idea that one just goes to a yoga studio for workouts doesn’t mesh with traditional practice at all. There’s a lot of spiritual components that get left out by the upper middle class white women who run studios.