That original Glacier API was infamous for being extremely cheap to write to but prohibitively expensive to read from. Something like 10 cents per list objects request or something ridiculous like that. Can't remember the specifics but I do remember reading blog posts from people that wanted to restore a couple files and had to pay several thousand dollars for that.

I believe that they did alter the pricing at some point. Regardless, the move to just a storage class on S3 made everything much simpler.