Here's why:

* Smaller size: Lithium is the smallest alkali metal. Its smaller size means its outermost electron is more tightly held by the nucleus. This makes it less reactive compared to larger alkali metals.

* Higher ionization energy: Lithium has a higher ionization energy than the other alkali metals. This means it requires more energy to remove its outermost electron, making it less likely to participate in reactions involving electron transfer, like the reaction with water.

While lithium does react with water, it does so much more slowly and with less vigor than sodium, potassium, rubidium, and cesium.