I think the low temperatures are due to two factors. Low temperatures slow reactions. I think self condensation reactions are the most likely problem. For example, if you are making an enolate of a ketone, low temperatures will decrease the amount of aldol reaction you may find.
The second reason may be trivial. As Disco stated, he made enolates a higher temperatures. If you were to prepare an enolate, you would most likely find a procedure that used a low temperature. Few chemists will embark a temperature study to determine the temperature sensitivity for their reaction. Many reactions become performed similar to original publications. That doesn't mean that for a different substrates, base, etc., that a higher temperature or other conditions don't work, but more likely they have not been optimized.