I don't think your speculation is completely unreasonable, but I just want to point out that consumer preference as revealed by current, actual reality only provides evidence in favor of my side of the argument. It's totally possible that the manufacturers are completely wrong about consumer preference and they are acting against their own interests by making the batteries non-replaceable, and somehow none of the manufacturers noticed this or were able to successfully take advantage of it to gain market share. But, I think that would be a pretty surprising thing if it turned out to be true.

Usually, in consumer electronics, the unencumbered market tends to gravitate toward what people actually want to buy. Totally possible this could be an exception to the rule, but I doubt it.