Okay here me out. Imagine its like 101F outside (this temperature is hot to humans, really hot). If you were to put your phone in your sweaty pocket screen-to-thigh you will get condensation on the screen (due to being pressed against the leg, no ventilation style). The condensation might fog up your screen protector if you have other than the adhesive glass type. Additionally, any pocket lint in your pocket will get stuck to a sweaty thigh phone, making the screen gross and hard to see/use. The above principle applies for shirt pockets.

I used to be like you but recently pocket dialed 911 so I switched to the bottom right method.