After a half-lifetime of involvement as a publisher, I've concluded that many join the 'pioneer ranks' with good intentions - to reach others in the community with the religion.
But, if a full time pioneer is honest they would admit that they do it for themselves. They like the title, position, special meetings and training schools.
Listen to interviews of pioneers at the assemblies. One question that is ALWAYS asked is "please tell us how full time service has benefited you spiritually."
ginger