Using poorly stored condoms. Heat, direct sunlight, and friction are some of the biggest threats to a condom’s durability. You should avoid using condoms stored in your wallet or glove compartment for long. The friction and heat in these areas might contribute to breakage. Condoms are meant to be stored in cool dark areas, away from direct sunlight.
Why? Beats me.
https://www.webmd.com/sex/birth-control/what-to-broken-condom