why is pmos better for passing logic 1?

If you try to pass a logic 1 with a npn transistor by connecting it as an emitter follower and driving the base with that same logic 1, you will get a full diode voltage drop across the transistor... the transistor is "diode-connected" (base connected to collector). The pnp will have a smaller voltage drop when you connect the emitter to logic 1 and ground the base (through a current-limiting resistor, of course). The voltage drop across the collector-emitter is much smaller then.

For logic 0, the situation is reversed.

Oops, I just noticed you were asking about mos. The situation is even more pronounced for mos than bipolar. How are you going to turn on an nmos device when the drain is at the top rail? You would need another voltage supply higher than your logic 1.