[BulletproofHeart]

I think it's to do with the stability of the enolate at that temperature which can be attributed to the strength of the O-Li bond. I think that the O-Li bond is stable only at low temperatures but I'm not entirely sure why.

Please correct me if I'm mistaken

[discodermolide]

I think it depends upon the enolate and the reaction it will undergo with a substrate. Usually the low temperature is required to control stereochemistry.
I have made lithium enolates at RT and even higher temperatures.

[Sircodekill]

I think it's to do with the stability of the enolate at that temperature which can be attributed to the strength of the O-Li bond. I think that the O-Li bond is stable only at low temperatures but I'm not entirely sure why.

Please correct me if I'm mistaken

low temperature gives you the kinetic product and high temperature the thermodynamic product. The OLi bond is stable but not for long time, with low temperature what you do is freezing the molecule vibration and movement enough to give time to the carbon α to react.

[discodermolide]

I agree with the thermodynamic vs kinetic control.
Lithium enolates can be prepared and kept for a long time under inert conditions. The Li-O bond is not a bond but an ion pair in this case surrounded by solvent molecules, for example THF or ether, which also help stabilisation of the enolate.
As I said it depends upon what you are going to do with your enolate.

[orgopete]

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.