They just might not be used to them. The way we do it with our couch is to literally buy 4 of those foam stairs and place it all along the front, and give them no choice but to use those stairs. For your bed, if you haven’t already, you can train them to use the stairs going down using treats.

I believe flat ground is more comfortable to them, so I do recommend stairs instead of ramps; do take me with a grain of salt, though, for I am no expert.