Why solids have negligible kinetic energy?

Its NOT.Kinetic energy is the energy of mass in motion. Two equal masses, one of a fluid the other solid, if moving at the same speed, will have EQUAL amounts of kinetic energy.

In terms of micro kinetic energy - the energy of vibration of individual atoms or molecules - otherwise known as heat - in a solid the packing structure limits the amount of vibration possible which is why as heat increases the solid melts and then the liquid then turns into a gas. However, again the micro kinetic energy in a solid is not negligible. Would you want to pick up a glowing iron bar?