I suppose so are we, as we here, as we would not be writing about it had we not found it interesting 
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Emma Grede -who was a good and charismatic interviewer for this line of podcasts btw- asked her about that [sold out]. As a business woman she knows very well that marketing works that way. But Meghan simply responded that it was such a 'surprise'. So it seems the Duchess does not regard it as a marketing tool.
An odd moment in the Grede podcast was when Meghan was asked what she had learned or would differently - in other words asked to reflect on herself. The response was simply odd: that she wanted other people to be more honest about her.
Meghan also said she would discontinue her own podcast so she would not be 'spread thin' and could focus on her company. In general people don't stop projects that are a great success IMO.