What' so great about CMOS?
CMOS (complementary metal oxide semiconductor) logic has number of desirable characteristics:

High input impedance.  The input signal is driving electrodes with a layer of insulation (the metal oxide) between them and what they are controlling.  This gives them a small amount of capacitance, but virtually infinite resistance.  The current in or out of a CMOS input held at one level is just leakage, usually 1 &micro;A or less.

The outputs actively drive both ways.

The outputs are pretty much rail-to-rail.

CMOS logic consumes very little power when held in a fixed state.  The current consumption comes from switching as those capacitors are charged and discharged.  Even then, it has good speed to power ratio compared to other logic types.

CMOS gates are very simple.  The basic gate is a inverter, which is only two transistors.  This together with the low power consumption means it lends itself well to dense integration.  Or conversely, you get a lot of logic for the size, cost, and power.