Amphetamine is generally considered speed however amphetamine has been quite rare since late 90s when methamphetamine precursor availability rose above amphetamine precursors availability.
So i think you mean meth. However, the above is commonly not understood, so speed is often sought. A user is often seeking a white powder and expecting it at a roughly consistent price. This is rarely speed though. In most cases it is methamphetamine cut to and with a powder.
If you mean why is meth ordinary, then its your source. MSM is commonly used to cut meth in Australia, but good meth is still very prevalent.