I see people in competitive telling me to give them the 2nd half and now I've seen it in pro play. Why do people fill it to half and then let a team mate defuse the 2nd half?

I feel like I don’t belong in my rank. All last act I was hovering bronze 3 (bad I know but this is my first fps) this act I placed silver and was thrilled, felt I deserved it with how I was performing. I than went on huge win streak and am...