This is slow for the same reason things like Angel's Flight in LA, and whatever that thing is called in Pittsburgh are slow: it is cogged railway, at least in parts.

https://en.wikipedia.org/wiki/Rack_railway#Abt

The Glacier Express also has lots of sections on regular (narrow gauge) rails, so it is not a simple cogged railway.

The general class is called Steep Grade Railway:

https://en.wikipedia.org/wiki/Steep_grade_railway

San Francisco uses a cable system to climb it's grades, but it is of the same general class.