The clauses may both be declarative yet lack the unifying relevance required for coordination. A sudden unrelated report about the weather inside a tightly argued scientific explanation neither extends nor reinforces the argument.
Here wāw could suggest an unintended partnership between unrelated judgments. The reason for separation is the absence of the relevant semantic bond, not a difference in sentence type.
Conversely, separation may also occur when two clauses are extremely close in meaning. So the mere absence of a conjunction does not always mean their meanings are unrelated; the next category explains the opposite situation.