I used to work retail with someone who would regularly help parents that brought their baby into the store. Every time the baby would shout gibberish while he was having a conversation with the parents, he would immediately stop what he was doing, look right at the baby, and say matter-of-factually, “I completely agree.”

When confronted with a statement like that I’d immediately start arguing. “But why don’t you like frogs? Frogs are so cool!” Etc. Those are the best conversations. Adults never try to come up with reasons to dislike frogs on the spot.

I guess what’s happening developmentally is that they’re practicing having conversations and you can do that in form (I speak then you speak then) without having decipherable content down.

I remember being shocked to hear a friend tell his 4 yr old kid it was against the rules to not make sense. Six years later, kid does make sense a little more often. Ymmv