This is strange. They ran into trouble merging the sales organizations. Two product lines doesn't mean you need two sales organizations, even if they have different demographics and need different types of ads. Why sell the same customers twice?
Does Youtube have a separate sales organization from Google Ads?
Your point has merit, but I would argue that YouTube has a much broader audience than tumblr. I assume this would make it easier to have a centralised sales team. (If they actually do)
Does Youtube have a separate sales organization from Google Ads?