Not sure if this applied universally, but I remember for years and years the common knowledge was that plastic caps are unrecyclable for some reason, and there used to be separate bins to toss them at recycling centers. That’s no longer the case, so keeping the cap connected to the bottle is one way to demonstrate that they should be recycled together.
(By “recycled” I mean most likely shipped to Southeast Asia to then most likely just find their way into the ocean)
Which is apparently all the time, especially when people are looking for ice cream.