Shariar was a great choice for Keysight honestly. He has the background and experience to explain the technology involved. Additionally, his company Bell Labs would be likely candidate to purchase such a beast. I would also guess, that one of the department heads of the company may have some influence in what kind of equipment they requisition (if he felt such a scope would benefit their research).
Dave on the other hand, while entertaining isn't going to buy one anytime soon, nor is most of his audience. I'm not saying that is their exact reasoning behind letting Shariar do the reveal, but it wouldn't surprise me if his company and location in it factored into their decision. Personally, I think they made the right choice, and I enjoy Shariar's content immensely.