I think as you said it is a survival instinct. It is easier to know what you want to run away from than it is to know what you want to run towards.

I also think that when we depict hell we imagine physical suffering which is easy to visualise and conceptualise. In contrast when we imagine heaven we think of a deeper satisfaction than something physical. A vast sense of boundless love and gratitude and connection. Who has any idea how to depict that? How do you conceptualise and convey true unbounding love and connection on the scale of the infinite?