Why doesn't my 2010 focus allow me gun it when it starts slipping in snow? It makes it impossible to get out of even a tiny bit of snow. My civic never got stuck because I could always just gun it, but my focus never gets above 2k rpm
There's nothing wrong with the vehicle, from what you've described. It sounds like it's doing exactly what it's supposed to.
I'm not sure you understand how to get out of a slide (or snow), which admittedly isn't particularly uncommon. "Gunning it" won't help, because your wheels are more likely to spin, which just tends to dig you deeper into the snow. Rather, your Focus is forcing upon you good habits, by not risking a red-line and by keeping your revs low. Traction control is probably what's holding it back, since it doesn't want you to spin, but I would not suggest switching that off until you're comfortable escaping snow with it on.
To get out of snow, you want to be careful of torque. You want RPMs low, and you want as little wheel spin as possible. It's good to "shift" up into higher gears, like D1 or D2, or if you have a manual override, head to second or third gear. Those will reduce spin and push you out more comfortably.
If you've gotten out of snow in the past with brute force (and I'm not disputing that it's possible), it's been mostly luck. You can also sometimes dig away enough snow that you hit the ground, which is where you actually get traction (assuming it's not lined with ice). But that won't apply in deeper snow or where there is ice, so I wouldn't suggest making a habit of it.
It is quite possible that the traction control is limiting the engine power. The control module is monitoring the wheel rpm, vehicle movement and the engine rpm. If it detects wheel speed beyond the set parameters it slows the engine speed until traction is achieved. You may see a flashing light on the dash. Typically it is a triangle with an "S" shaped symbol. I am not sure about all the Focus models but most traction control can bedisabled by pressing the light.
Ford have from time to time have controlled engine revs in instances like you describe. Doing so protects the CVT transmission from damage. For a while they also controlled the engine speed from idle whilst stationary, to a max of around 2500-3000rpm, across thier automatics.
This is traction control working, doing what it's supposed to do.
On snow, however, it can be usually best to deactivate it, as most cars can do. It will help when getting out of the snow from stationary (if you have manual gear control, at least), but when on the move and uphill, you actually want to be able to control your wheelspin freely. If the engine cuts power when wheelspinning uphill, you risk losing speed and coming to an unavoidable halt, getting out of which may be difficult.
A great part of the ability of driving in the snow, particularly uphill, consists on being able to keep a steady speed while at the same time steering the car in the right direction. Most 4x2 Traction Control and ESP systems are yet nowhere near a good driver when it comes to this, so disabling them on the snow will help if you know how to drive on snow.
As a sidenote: on snow, there is nothing you can possibly do if you are not equipped with good winter tyres. Most people still fail to see that.