Killing ants: Why cut vinegar / rubbing alcohol with water / dish soap?

Title: Spray alcohol, feed. The end!

A spritz of rubbing alcohol will instantly kill any insect. Plus, because alcohol is a disinfectant, there is no need to rinse. The alcohol simply dries up in a minute or two. So after you have killed the trail of ants by spritzing the alcohol from you spray bottle; lay down a mixture of borax and sweet-smelling maple syrup to kill the ant nest.

Here’s how: Put a sprinkle of borax on a formed piece of tin foil the size of your thumb ... then squirt 1 tsp. of the maple syrup in the middle. As the ants track over the borax they are poisoned. Then after they eat the syrup they go back to the colony with their "take-out" special for all the rest of the colony and Queen to eat. After a few days … no more ants because everybody dies.

(One final tip about the spray of alcohol. It will also kill flying nats, miscotos, house flies, and more ... they fall right out of the misty-fog-spray of your spray bottle.)

When vinegar and water is used, the recommendation is to coat the entire surface in the vinegar/water solution. As you observed, when you spray vinegar, it does not form a continuous coat but separate blobs that the ants can navigate between.

Adding soap reduces the surface tension and allows the mix to spread out more.

I suspect the recommendation is to cut with water to prevent damage to the surface you're using the mix on. You don't need a highly-concentrated mix, you're just disrupting the pheromone trails left by the ants - and those scent markers are tiny so you don't need much to disrupt them.