Why do bacteria adapt quickly to antibiotics but not to much more common threats?
Antibiotics usually target a single protein (most commonly components of the ribosome machinery). If you have a large population of bacteria, there are bound to be cells with mutations in the gene encoding for the target of the antibiotic that render the antibiotic ineffective. Microbes also have drug efflux systems that can help with resistance to antibiotics. Temperature on the other hand has broad lethal effects from disrupting the cell membrane to damaging DNA and affecting the reaction rates of vital enzymes so that it's impossible to adapt in such a short time by gaining a few mutations.