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.

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... :)