You are wrong there. If you have an Android smartphone, look at the charger, chances are it says both
[email protected] (or around there) as well as 9V or another voltage. Samsung uses 9V, OnePlus is the only brand I know that uses 5V for fast charging.
Many phones now have fast chargers that support charging at 30W or even more, 5V simply isn't capable of handling such current without making the cables excessively thick (and then you could not use just any USB cable, you would have to use the special one the manufacturer gives you, or risk a fire when the cable melts if there is something flammable nearby), USB cables are made with extremely thin wires.