Second, these analyses are usually oriented around an effort to either prove or debunk the existence of a particular type of lane, usually the liberal or moderate lanes. But voters come around to their decisions for lots of different reasons. Some voters do vote on the basis of ideology or policy. Some vote on demographics or identity. Some factor in more abstract considerations like “leadership” or “electability.” And some just haven’t thought deeply about their choices yet. When candidates are aligned along several different dimensions — for instance, Pete Buttigieg and Beto O’Rourke have much in common in terms of their demographics and their policy platforms — you can see especially strong correlations in which voters support them, with one tending to rise or fall at the other’s expense. But most of the time, it’s messier, with different threads pulling in different directions.
To extend the lanes metaphor, you wouldn’t expect to see a single, parallel set of lanes connecting all voters in the Democratic primary. Instead, you’d expect something more like a complex, multi-modal transportation network, where some parts of the network are more robust than others, but there are a lot of somewhat redundant options. This doesn’t mean that paths between different candidates are irrational or random, any more than the choices of, say, Manhattan commuters are. But they might look chaotic in the aggregate if you don’t recognize that different voters have different priorities and take different routes to get there.