One on one pitches are more conversational. So the slides are designed to be something you have a conversation about, not something you simply present.
It's really the short Demo Day type pitches that require the most design. A Demo Day pitch can't leave obvious questions unanswered, because there is no chance for anyone to ask them. A pitch deck for an hour long VC meeting doesn't have to be so watertight, because if investors have questions they can ask them.