At first anyone could associate this issue with sweating and then hotter the temperature it could be worse. It also suggests how important the sock fiber is because some transpire better than others, like shoes. With a good shoe design, the sweat should be allowed to leave without creating problems of any kind.
With cheap fibers or shoes, the quality of materials and design in general perhaps is not the best possible creating differences from whom invest in research and development to do it right or those companies that follow other procedures and goals.
The main culprits of foot odor are little forms of life, the so-called microorganisms. Like it or not, a human foot is like a habitat or say if you prefer ecosystem —farm sounds a little strange— where there's more than skin. These microorganisms emit this characteristic odor and that's the proof that they find the necessary nutrients for being massively replicated, principally sweat.