that's not how language works though, in human language (i know this can be confusing) d and D are the same letter just in different forms.

It's one thing to have case sensitivity in programs doing data manipulation, that makes sense because you don't want the program to accidentally use the wrong files without supervision.

But when you have an interactive prompt you know what you're doing, you can see if you entered the wrong directory, and you're generally going to be working in directories that you have yourself organized.