Where did I go wrong with this frame painting procedure?
Painting is tough and the artist in me (tongue-in-cheek) is never satisfied with finished product. Your prep seemed meticulous enough and you express satisfaction with the finish where it hasn't been marred. Given the work put into the prep, why go with bargain paint and risk the poor quality of it?  Give you props for using the same "brand and series" of paint.  That tip is frequently included in DIY paint tutorials. 
The two most popular brands of spray paint here in Midwest, USA are Krylon and Rust-Oleum. I bring this up to share a couple of things common to the directions for use printed on these cans. Despite the myriad of differing formulations and applications within a brand here are some common advisories they share: Priming is especially recommended on bare metal or wood.  Apply multiple, thin coats, waiting a few minutes between.  Apply additional coats within one hour, OR AFTER 24. Some types will state "recoat (or apply clear coat) within one hour OR AFTER 48."  This is under ideal drying conditions of 50% humidity and 70°F.  Finally, it's commonly noted that on plastic, "maximum paint adhesion and durability is achieved in 5-7 DAYS."  I realize your bike is not  likely to be plastic but I think that tip can lead us to believe that the paint will continue to cure and become most durable quite some time after the "ok to handle in such and such hours."  If your paint job is being marred right down to bare metal as you say, the paint is not nearly cured enough. Certainly 12 hours isn't enough time to expect it to hold up.