Why is heel calluses worse in the summer?

I feel like the white calluses on my heels get worse when I wear sandals. Is it athlete's foot rather than just dead skin? They appear white and are incredibly itchy. I'm curious how everyone takes care of their feet.

I want to completely get rid of dead skin cells, but after a while, they keep coming back again and again.

I bought an exfoliating scrub at Daiso.

Please give me some maintenance tips.