Probably because OpenAI is the best at this than any other player in the game. They’re on their way to replacing Google as the #1 search engine. Instead of “google it” it’s going to be “gpt it”, and we all know who “gpt” is.
For me the AI seems to actually understand the meaning of my search term and is usually accurate and helpful. It is an improvement over how bad Google had become when it randomly deleted search terms.
Hmm... it doesn't jump for me. There's a fixed amount of space reserved at the top of the screen and the AI overview loads into that. It only expands if you press the "Show more" button.