Thermal Admittance and Surface Temperature Fluctuations

There's a slide in one of the lectures that asks "why are soils with low thermal admittance subject to extreme surface temperature fluctuations?" I am confused about this because if a soil has low thermal admittance, doesn't that mean it doesn't accept and release heat as easily and therefore the soil's temperature would not fluctuate drastically?

Thanks in advance!

In organic soils (that have low thermal admittance), as surface temperature rises, a temperature gradient develops, causing some (but slow) heat conduction downward (due to low thermal conductivity). The heat energy tends to remain near the organic soil's surface. The increased heat energy content makes soil surface temperature rise very high, because these organic soil also have a low thermal capacity (Cv) means that even a little increase in soil heat content will cause a large increase temperature. Remember, organic soils are good insulators, but poor conductors of heat.