It is much much easier to measure voltage than current. Voltage can be measured by attaching a scope or voltmeter in parallel with the equipment without cutting any wires. So, it is a "non-destructive" measurement technique. Whereas, current has to be measured by attaching the ammeter in series for which you have to cut a wire which makes it a "destructive" measurement technique. You have to repair your wire after you are done measuring.
PS: By "destructive" I mean that you have to cut a wire to measure, not that it interferes with the signal.