chokes usually flow from the outside of the cage to the inside so that the fluid hits itself in the middle and then flows vertically down.
Hence and angle valve then means that the flow doesn't hit the sides of the valve as it exits.
Nice, neat, cheaper to build. What's not to like?
Plus in many wells the choke valve is high off the ground and you want the pipe to run along the surface so you need to bring it down to ground level any way. This way you only have one bend or target tee to do that.