I don’t know if I agree with this – the way we do it, indented blocks are for “code” that you don’t want syntax highlighted, and fenced code blocks are for code that does need syntax highlighting.
So it’s a feature from my perspective.
We used to syntax highlight everything by default on Stack Overflow (we still might actually) and that was acceptable since it was a site for programmers. But I doubt it is a good idea at all for a general audience.