Several reasons:

(1) Think in terms of object oriented programming. You want A, B, C, ... to be atomic, basically. I mean: you can update A without having to change B, C, D, ... Otherwise if you build a linked structure, your work grows exponentially over time. Not feasible. (Dan Ingalls's great contribution to computer science was this concept.)

(2) Some people find the list useful. Don't care for the post that links to it. A good number of upvotes are because it doubles as a "recommended" list. That's intentional.

(3) I've also found putting the list at the bottom prevents people from clicking the upvote; they move to the next post. My preferences are to cite in a complete manner. But that means 10 to 20 references however.

(4) 1000 words of many of my posts was the references list when placed at the bottom; not ideal.

(5) A very major use case of an immutable archiving system is that you can update your previous publications. My view of Steem is arXiv but semipopular. Not everything that is worth making immutable and timestamping is appropriate to throw on arXiv, BioRxiv, etc, etc. Or under your real name. Like if I want to blog about something political or something with the same account.