Why does electrical process signals often take the form of a current instead of voltage? two specific reasons for this.

Electrical process signals previously were mainly presented by voltage. It is only with modern day digital electronics that current replaces voltage as the signal.

This is because the basic building block of ICs is transistor which is driven by current; instead of voltage. Voltage signals also have the disadvantage of signal loss over distance due to parasitic resistance. Current signal requires more power to be transmitted in long distance but otherwise does not suffer signal loss.