Why was poison a popular way to get rid of someone

Poison spreads around the body quickly and it is less suspisious as you can put it into drinks or food

because it kills them usually without any obvious visible signs

Explanation:

poison has to be ingested and taken in by the body so it is easy so sneak into someones food or drinks. Many types of poison are tasteless, colorless and odorless. Venom is a less popular way because venom is a.) hard to get, and b.) it has to be directly delivered into the bloodstream so if you swallow venom, it will not kill you but poison will.