Why doesn't ⌥ (option)+click bring up the context menu? Does anyone know why ^ (control)+click was chosen to trigger a context menu, rather than ⌥ (option)+click? Is there any history surrounding this?

To me, an alternative method of clicking that brings up a menu of options seems most intuitive if triggered by ⌥ (option)+click, especially considering that key is also known as ⌥ (alt).
The option key has been in use on Macintosh computers long before there was a control key, since the option key was always used for alternative input of characters with diacritics, like "å".

Apple always tried to force developers into not hiding away functionality into contextual menus and thus did not include more than one mouse button for quite a long time. I think it was once applications gained complexity and needed to offer contextual menus for better usability, that Apple decided to include a control key for the first time. 

In short: The naming of the control and  option keys are meant quite literal: one gives you access to optional input and one gives you access to controlling the interface.