Why are mountains narrower at the top than at the bottom?

my guess is because mountains are formed from earthquakes etc right? like convergent boundaries. so the two tectonic plates go towards each other like this -><- and they push each other upwards. over time, since the peaks are so high up, whethering carves the peak into a point.

sediment layers stop spreading when they reach a barrier or they run out of sedimentary material. lateral spreading is the movement of gently to steeply sloping, saturated soil deposits caused by earthquake-induced liquefaction. i hope this . : )