USB micro (not sure if you're getting micro confused with mini, but doesn't really matter) only supported data transfer, not video transfer (like HDMI). Some USB-C ports are data only, but it theoretically supports more than USB micro was ever capable of.

For example you can buy a USB-C to HDMI cable for a few dollars, which could theoretically plug your phone directly into your TV (if your phone supports that). But a USB micro to HDMI cable was called an "MHL adapter" and was expensive and only worked on specific MHL capable phones like this one. It has a separate box that requires its own power cord in order to work, it's not just a simple cable. USB-C should, in theory, eliminate the need for such a thing.