You know you're grasping for straws when reality and facts are considered fictional deflection.

As for the questioning --

When the reason you do something originates from personal gain rather than viewing personal gain as a byproduct of a shared gain and/or when there is an intentional lack of consideration for others due to prioritizing oneself. That is selfish / self-centered / ego-centric / whatever synonym you want to use.

I think I've provided ample examples of this but I will restate the situation you are defending. Queuing for a dungeon with the goal of farming tomestones and then telling others that joined with a different purpose that they are not entitled to pursue their own motivations and should instead sacrifice their time for you. Your reason for queuing originates from personal gain, farming tomestones, rather than as a by product of an urge for a good shared experience / a fulfilling run for your party-mates. You clearly prioritize your own tomestones and time over the will of the leaver. SURPRISE! Their motive for leaving is probably the same!

As for what's not selfish -- doing anything with the primary goal of accommodating others.

I mentioned that I join Savage helper parties. The only gain that I personally get is more experience with the content and networking -- the former is the byproduct of a shared experience gain and the latter is a byproduct of what is hopefully a fulfilling run for the people I'm helping.