The screen of your android phone is supposed to connect to the motherboard underneath it, and the ports on the screen are located at the bottom of the screen, so manufacturers have to keep that chin to give space to the cables that will be connected to those ports.
There is a way around this and that is for the manufacturers to bend the screen inside, just like on the Nothing Phone (1), or the iPhones, but it adds to the cost of manufacturing the phone, so it isn't regularly done. Notice the chin on both phones below
