The shortened nickname “pot” comes from the Mexican Spanish word Potiguaya or Potaguaya means “marijuana leaves​

My understanding was it was popular amongst the gay community in previous centuries. As they were socially ostracised many would cross the border where they were known as 'Mary Janes' or Maijuannas. Ultimately their drug of choice was given that name.

Long after it's legal everywhere the vestiges of the culture that brought spleef to the mainstream and had to dodge the cops will remain. It has so many names. It's about obscuring what you're really talking about in case you're overheard.
[time.com]
"There are at least 1,200 slang terms related to marijuana"