Why do we need to mount on Linux?

I understand what mounting is in Linux, and I understand device files. However I do not understand WHY we need to mount.

For example, as explained in the accepted answer of this question, using this command:

mount /dev/cdrom /media/cdrom

we are mounting the CDROM device to /media/cdrom and eventually are able to access the files of CDROM with the following command

ls /media/cdrom

which will list the content of the CDROM.

Why not skip mounting altogether, and do the following?

ls /dev/cdrom

And have the content of the CDROM Listed. I expect one of the answers to be: "This is how Linux is designed". But if so, then why was it designed that way? Why not access the /dev/cdrom directory directly? What's the real purpose of mounting?