Pratyekabuddhas, Shravakas, and other Nirvanis (of whatever name) still have karma and subtle forms of ego. They have gained the right to enormous bliss in Nirvana for extended periods of time. During such time, ego and karma are only suspended, and they are not interacting with the lower realms (where we are).
Nevertheless, they return every once and a while to a physical body, to karma, and to whatever remainder of ego they have. During this time they are in danger of falling and creating lots of ego again.
They may look like perfect saints to us, but this is because we are so asleep. A fully awakened master can see that those of the Spiral Path still have imperfections within them.
The term 'selfish' has to be understood in context. They may be very compassionate when compared to any ordinary person, but in comparison to the Direct Path Bodhisattva, they are selfish.