It’s pretty simple. If they didn’t want to live, why didn’t they self-immolate in a place where no one can put them out? By choosing a place with people they implicitly accepted that there might be people there that would try to not let them die. Maybe they even subconsciously hoped to be stopped.

Stopping physical harm happening to others is a very natural way of behavior. It’s almost certain it happens when a couple of people are present. You can’t ever blame someone for trying it.

And then there’s the case of open fire being able to spread and hurt others.