Favored Conditions of Bacterial Growth
The idea that bacteria thrive in warm places is mostly biased from a human perspective. Human researchers will tend to care more about bacteria that cause human disease. These pathogenic bacteria can replicate in/on humans at ~37 °C (which is warm). As Dexter points out, bacteria can grow at other temperatures.

But I'd go deeper and consider proteins (and other macromolecules) in the cell. For example, the enzymes that carry out many important processes for the bacteria (such as DNA polymerases that build the DNA) are most active at certain temperatures: in E. coli or humans or dogs that's ~37 °C; for a thermophile it's warmer. See below: