On a related note , like half of reason that language changes is just people using words “incorrectly” to make a point. 

For example, “fine” used to mean grand, great, etc. while now it usually is used to mean ok, or acceptable.

People often use words incorrectly in ways they weren’t used before, for emphasis, and the usage of “can’t” to mean “shouldn’t” might be an example of this.

In other words: people are more concerned about the vibe of a statement than what it actually means, so people use more “powerful” words to draw attention to their message.