Why equipment grounding and bonding connections are never made to the hot water piping systems.

The Hot water piping is independent of the cold water pipe and does not exit the home. The hot water pipe would not carry the charge out of the home to be discharged unless you bond the hot water pipes to the cold water pipes.

NEC Code requires that the connection to the cold water pipe so that the current can be carried outside and returned to the earth. Effectively, this provides a short circuit (zero resistance) pathway to protect your structure and people inside the structure.

Because hot water pipes begin at water heaters, and are often insulated or otherwise not electrically continuous to earth ground.

However, the NEC requires hot water, cold water, and gas lines to be bonded together. This is usually done at the water heater, since all three are present there.