There is significantly more spectrum available for wifi in the 6ghz band than in the 5ghz band, so even if we moved everything off of 5ghz and ignored the attenuation benefits of 6ghz, we'd still have significantly less congestion on 6ghz than 5ghz wifi. In my apartment, my laptop can see ~50 wifi networks, we need some spectrum elbow-room to spread that out.
Even if you halve that, how many online activities are going to make use of that bandwidth? And if you have a 2x2 client, you double it anyways. A 1x1 40Mhz using 802.11ax will give you a max PHY of 287Mbps. How many activities use >100 Mbps, especially continuously?
Off the top of my head: certainly downloading a new game or software updates can eat up those bits, and photo/video editing or creation (local NAS or uploading) it might be useful; are there any other activities that use that?
As I commented elsewhere: it would be great if residential Wifi devices defaulted to 40 MHz.
Completely independent of bandwidth, higher frequencies also fall off faster. That's bad if you are trying to cover max space but good if you are trying to avoid noisy neighbors.
They are if they're in an urban environment (which is 80% of the population of the United States). Maximizing your channel width only makes sense in suburban/rural areas. You can get a much more reliable connection by using a smaller channel width.
https://en.wikipedia.org/wiki/List_of_WLAN_channels