Friend requests

I often wonder what prompts people to send a friend request. What's the point if they don't then interact? My about Me says to leave a message otherwise I will probably ignore the request. Clearly people don't read it. So, what is the expectation if they don't give some idea of why they want to be a friend &/or don't engage? I deliberately keep my friends list short. If there is only limited contact early, I delete.