Why you can't create CON as a folder name?

It's not CON only, there are many names that cannot named like :

CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9

because they are commands on MS-DOS system and naming folders or files like it may results in errors and system unstability.

CON -by the way- stands for CONSOLE ^_^

Have a good day