Why is there no lower temperature than absolute zero?
Absolute zero means that we are measuring temperature relative to the coldest temperature possible of 0K.
Temperature is a measure of the average kinetic energy (KE) of particles. This basically means how much the particles are moving. Particles that move faster have more KE, particles that move more slowly have less KE. Particles that are not moving at all have no KE.
At 0K (-273.15 Celcius) all particle movement stops.
To have a temperature lower than 0K would have to mean that particles have negative movement. I guess that would mean that they travel into some other dimension - just kidding :)
Since negative movement is not possible, there is no temp lower than absolute zero.