Question: why pmos gives strong 1?
Answer: So the maximum voltage level that the output node can be discharged to is |Vthp|. So an NMOS passes weak 1 and PMOS passes weak 0 whereas no such situations occur when an NMOS passes 0 and a PMOS passes 1. So PMOS is good to pass logic 1 and NMOS is good to pass logic 0.