Snow is localised and melts into captured streams. It gets refilled because high alt + low temp preferentially causes rainfall/fog that replenishes the snowpack

Snow is localised and melts into captured streams. It gets refilled because high alt + low temp preferentially causes rainfall/fog that replenishes the snowpack. If fewer rain cloud condense on the peak then it just rains more dispersed which leads to much less efficient capture (some absorbed by the ground, some rains over ocean, evaporation is faster when you have water spread over large area so fraction of time spent in liquid form is smaller, etc).