Your language is a bit sloppy here: "the angular speed is rotating about an axis" doesn't make much sense, and I'm not sure exactly what you mean.
"but why is the velocity parallel to the axis?": by this I guess you mean "why does the angular velocity vector point along the axis of rotation?".
If so, it's for two reasons:
1. the axis of rotation is at right angles to the plane of rotation and hence uniquely defines the plane in which the rotation is taking place, and it's also constant (it's hard to describe the rotation in some other way with a vector; for example, the velocity vector of any point in the plane is always changing direction so don't make good candidates for describing a fixed quantity).
2. when you point the vector in that direction, it makes the relationship
v=ω×p work out correctly as long as the velocity and angular velocity are related by a right hand grip rule (curl the fingers of your right hand the way the plane is turning, and your thumb points in the direction of the +ve angular velocity vector).