We've even had word processors for over 40 years, why would we suddenly need mouse support to write rich text?

Editing rich text without mouse has always been a thing, Markdown isn't something that suddenly created some fancy new rich text without mouse experience.

It obviates the need because it is not rich text.

Yep i use the mouse and I'm very fast with it. I bet I'm faster with it than you are with your keyboard ;-)

It's not the speed, it's saving the carpal tunnel for video games... :)

Well most rich-text have the common shortcuts tho, like ctrl + b to put text in bold.

But the way that is represented in the file format isn't standard, which means it may not be interoperable.