Comment by Dwedit

Meanwhile Shift-JIS has a bad design, since the second byte of a character can be any ASCII character 0x40-0x9E. This includes brackets, backslash, caret, backquote, curly braces, pipe, and tilde. This can cause a path separator or math operator to appear in text that is encoded as Shift-JIS but interpreted as plain ASCII.

UTF-8 basically learned from the mistakes of previous encodings which allowed that kind of thing.