Ok...
Soda is not a made up word. It comes from how it was originally made by adding sodium bi-carbonate to water. But it was originally invented by a guy called Priestley in 1772 by adding sulfuric acid to chalk in water to produce carbon dioxide gas, and he called his invention "Soda Water"
Pop comes from some of the first bottles used to bottle Soda Pop. The lids would make a "pop" sound like removing a cork from champagne bottles.
In places like Canada, soda is used more for soda water which is mixed in alcoholic beverages. People are kinda lazy, and they shortened it down from Soda pop to just Pop.
Soft drink simply means "Non-alcoholic" where as Alcohol is a hard drink. The reason for this is drinks like Ginger Beer which is usually non-alcoholic is a "Soft drink" despite having beer in it's name which is a hard drink.
In Alcoholic drinks the carbonation occurs through fermentation, where as in Soft Drinks carbonation is added chemically. See the difference?
Pop is a much more descriptive and better word.