Dermatophytes like to set up camp on skin because they feast on keratin, a strong, fibrous protein that makes up much of your skin (as well as nails and hair, where fungus can also thrive).
One of the most important things to keep in mind is that, besides keratin, fungus loves two things: warmth and moisture. This is why it so often holes up on sweaty feet. Tinea cruris (jock itch) likes to hang out around the groin, anus and inner thighs -- all good places to reside if you like warm, moist places. Candidiasis can be found in your armpits, under breasts and between toes, among other places.