Most mortals do try to avoid going to the hell/Gray Waste.
Most mortals do not “know” a hell exists. Know means to have evidence. What most mortals can observe is that there are other mortals that “believe” some afterlife with a hell exists. Most mortals observe structures and places that have been dedicated to the idea of some higher being or beings. A fair number of mortals have seen other mortals with unique powers, powers that those other mortals claim come from some divine being or beings.
Some mortals:
Don’t believe in the hell or just don’t care,
or think they can find a way around going there,
or just want their dessert now and don’t want to wait for a good afterlife.
Think that they are already living in the hell and objectively may be.
Believe in the gods of malice and think these gods will reward them.
Were good, but did one bad thing in a moment of some type of distress or extreme emotion and that sent them to the hell.
Were good, but did one bad thing and said, ‘well, I’m going to hell now anyway,’ and from that point on kept doing bad things.
Were good, but bit-by-bit started down a bad path and ended up doing things that would send them to the hell – example: stole food so their family could eat. Stole food/something and had to fight/defend themselves to get it and hurt the person they stole from/fought. Then hurt someone first and then robbed the person to make sure they get the thing. Maybe in the processing of trying to hurt someone but not kill they had to kill to defend themselves or ended up killing the person to get the thing. Then they just started with the killing first then rob the body. And/or then they just started killing for-hire as it paid and came with perhaps a certain amount of less risk than robbing. All of this harm being done, in their mind, for the sake of their family. This process maybe took months or years and they didn’t see how step-by-step they were changing.