There's more to anticompetitive behaviour than just buying out small companies...

Nvidia has huge market share and uses their power as a weapon, in ways that are anticompetitive.

For example, in the past, they ~~bribed~~ financially encouraged devs to implement over-the-top tessellation because they knew it hurt AMD cards more than their own. They even went as far as encouraging hidden, highly tesselated textures in games to do this. Such as full oceans under the ground, or highly tesselated hair being rendered on bald people, then turning the opacity down to make it invisible. All while still crushing performance.

More recently, Nvidia had the GeForce Partner Programme. Basically, Nvidia was trying to strong-arm partners into essentially giving ownership of their branding to Nvidia, and banning them from using it with AMD products. Also banning branding AMD stuff as for gaming.

E.g. under this scheme, Asus might only be allowed to use their "ROG" branding on Nvidia products, and they wouldn't be allowed to have "Gaming" on their AMD products.

Failure to join the GPP meant losing first access to GPUs, having less time to prepare for new launches, and worse pricing on GPUs bought from Nvidia.

(Fortunately, though 2 OEMs joined GPP, public outcry killed it)

Or how about Nvidia telling Hardware Unboxed and other reviewers that if they didn't give Nvidia positive reviews, they'd fuck the channel over?

Nvidia has done a lot of anticompetitive stuff.