Now the USA has 87 million cattle.

Private cattle ranches could never have competed with 30 million bison owned by nature, free for anyone to take.

Many ranches raise bison. And even deer.

Just because the population was wild then wouldn't have precluded ranching bison, or even cows.

How to you make a fenced off ranch when 30 million buffalo decide to stampede through?

You wrote it by yourself: you fence it off!

And how does a stampeding herd coordinate to move around a fence?

Buffalo will run off a cliff in the hundreds because those in the back can’t see what’s in the front.

Or because they've been driven from the rear and prompted by by a lead decoy to run toward a natural Ha-Ha, a drop hidden by the curve of the land.

https://en.wikipedia.org/wiki/Buffalo_jump

https://en.wikipedia.org/wiki/Ha-ha

There are second hand accounts from indigenous people, excavated bone sites with tools and spear tips, but reportedly no first hand recorded observations from Europeans of buffalo running off cliffs.

Buffaloes aren't exactly Main Battle Tanks you know: it's not that difficult to build fences that are able to stop them (it just won't be the light fences you have in mind).

Also, not voluntarily pushing the beasts to your fences is going to help a bit, since buffaloes don't run to cliff on their own…