Captain America: Civil War was a long movie with a lot of characters, but that doesn’t mean we saw everything. Even with a two and a half hour runtime, a lot of things had to be cut out. Unless you like watching five hour movies, sacrifices have to be made.
The video talks about some scenes that didn’t make it into the movie for various reasons. In some cases these scenes would’ve made the movie drag, in other cases some of these scenes would not have made sense. As the video says, the Ant-Man scenes were written before the Ant-Man solo movie ever came out, so things had to change to reflect what happened in that film.