Why was caltrop introduced?

Answer 1

If you are referring to the land weed (not the water chestnut caltrop) then it was probably not introduced intentionally at all. They have very resilient seeds that are well adapted to sticking to rubber tires. As such they pretty much grow at any major airport across the world as long as the climate permits. They also like to grow along bike trails.

Its growth is countered by a weevil that exclusively targets puncture vines such as these.