Or perhaps, unbeknownst to everyone in the world who uses the word 'vanilla' to mean 'mundane', vanilla ice cream actually enjoys far higher profit margins than all other ice cream.
It would be literally impossible for an aisle cap to feature every ice cream flavor available - there are so many that each flavor would have very little representation in the display, and the concept would fall apart as soon as anyone bought something from it. At that point, you're paying a bunch of extra money to send the message "check out our least popular flavors".
That's what I expect them to do, though. The most popular flavors, by definition, needs advertising the least.
The advertising costs the same whether you advertise popular flavors or unpopular ones, but you'll get a lot more sales by advertising the popular ones.
Go check out a grocery store, see whether the aisle caps slant towards popular or unpopular product varieties.
What's not implausible is the idea that one flavor of a product with several flavors might be located far away from all the other flavors. That happens all the time.