It has nothing to do with the enriched media. Incubation temperature has everything to do with the microbe you're growing. E. coli and most other pathogens affecting humans (which are the most heavily studied microbes) tend to have evolved to grow best at the temperature of the human body, 37C. Other organisms, such as yeast, grow best at 32C (or even lower). Trying to grow a thermophylic archaea at 37C would kill it - they require temperatures often near boiling. Most moulds grow quite comfortable at 25C. So, it is important to remember the natural habitat of a microbe before deciding on a temperature at which to try and culture it.