They provided two true statements, they didn't link them causally even if they could have done more to make sure people didn't assume that they were implying causation (or maybe they were implying that they think it's likely).

If I say "I hadn't done any of my homework in Calculus. I failed the class." Most readers would assume that the homework statement is related to the failure statement. Even if the real reason was the homework was with zero points and I failed the final exam because I left after five minutes to chase my future wife down before she flew home. That's the thing with language, it's not formal logic and readers make all sorts of inferences based on order and content of statements. That's what makes for good writing and reading between the lines.

I don't know what the poster meant, but drawing a conclusion that there is some correlation due to statement choice is normal.

> That is a post-hoc fallacy, implying LG sold poorly because it stuck with these design choices

No, clearly saying that LG tried all the OP was asking, but there wasn't enough of a market for it, so OP is obviously in the non-sufficiently profitable minority.

Smartphone market is much more complex than just ticking feature boxes. There is brand value perception, post-sales support and warranty, ecosystem, OS customisations, device exchange programs and other marketing strategies.

There might still be market for users looking for modular phones. Fairphone comes to mind in this aspect.

LG failing to provide a product for this specific market niche isn't enough of evidence to support the claim that the market itself doesn't exist, only that LG couldn't or had no interest in maintaining it.