I think this explains a lot. From the most recent Office Hours, RSC is interviewing Horton about his joint For/Against Calvinism project with Roger Olson. At about 7:50 in the audio, RSC has this to say:
Let’s focus a little bit on the Reformation traditions. The two great Reformation traditions, are the Reformed folk and the Lutherans, the confessional Lutherans. The founder of arguably the main representative body in North America of confessional Lutheranism, or at least one of them, the LCMS (Lutheran Church Missouri Synod) — the founder, C.F.W. Walther, his theology was so closely identified with Calvinism that he had to spend much of his ministry and life explaining why he wasn’t a Calvinist, and consequently excoriating Calvin to show that he wasn’t a Calvinist.
Maybe this is why Walther devotes six whole lectures against “The Reformed” and “the sects of Reformed origin?
This is followed by a very interesting discussion by Horton of how the LCMS arose out of a controversy over Unconditional Election, and why Lutherans are not Arminian, despite their rejection of some of our 5 Points.