Because you would need to know the code for å in all kb layouts, on all OS’s, even in a bare terminal with no way to just open the emoji picker, with or without special keys and no clipboard. Of course, tab completion or globs may help you, but not in all cases.
Try to select blåhaj.txt in a dir with blåhaj.txt and blahaj.txt present. Easy, ls blhaj.txt | grep -i blahaj.txt. Now with blåhaj.txt and bløhaj.txt. Not as easy anymore, but doable with tail -n1 or head -n1. Now do it consistently in a script. So you again need to single out the right string, or single char, and >> it into the script so you have the special char. Then you have a component that does not like certain special chars, so you need to escape it. All because one decided to use special chars as a file name/identifier. Using [a-zA-Z0-9-_.:;,] would be so easy.