The two main stimulants for this particular conspiracy seem firstly to be dissaproval of the relationship and its beginnings, and secondly being unable to conceive that an much older woman and younger man can ever sustain a long term relationship. But these things can and do happen, though not as often as the other way around.
i cannot begin to imagine why such conspiracy theories ( about Brigitte Macron and Michelle Obama) have taken hold in the first place? What are they trying to insinuate, and why? It just comes across as pointless, idle, malicious gossip.