That's the question everyone has. Something is on them that is not obtainable through the service provider. If by some miracle they are found we will have our answer. Either they were disposed of with purpose or taken. There has to be something incriminating to someone on them. Otherwise they would not have disappeared. JMO.
They (DB and JI) may not be versed in what can be determined from phone company records vs the phones themselves. And if they were staging a scenario where "they took the phones so we couldn't contact police" and hid their phones to fit that story, then LE's finding them on the property could be indicative of their fabricating such a story.