Because it supports (on WiFi 7) 320MHz channels. So there is double the bandwidth. 5GHz only supports 160MHz channels.
replyWouldn't it make more sense then to ask about high bandwidth channel support rather than frequency support? It's not the frequency that's important here.
replyHigher frequencies support higher bandwidths though.
replyI don't think the 2.4GHz band even has 160MHz free, for example. Literally impossible to support because 2.4GHz to 2.5GHz is all you get (100MHz or so).
5GHz isn't much larger than 160MHz. Like it can fit but some number of channels is better for everyone.
6GHz band is like 5.9GHz to 7GHz or something stupidly wide. Because of the new wider band, you can effectively have larger channels with fewer problems.