Well 5ghz requires more power, has less range, and needs its own antenna so for microcontrollers this makes it pretty pointless for devices that need range and low bandwidth for sending sensor updates, especially those that are battery powered. 5ghz can also have its own issues in cities if you have a lot of use of the DFS bands as well as being worse at traversing reinforced concrete.
Also, a 2.4ghz radio can also sometimes support other things like zigbee, BT, and BLE which can be used for other functions.
For what it’s worth, I have probably 50 WiFi devices and the majority of them are 2.4ghz sensors or switches and other low bandwidth tasks and I don’t have any issues, even when living in an apartment complex. If you are having issues you might need different hardware or more access points or something.
Anyway, all that to say that 2.4ghz definitely still has a lot of utility today.