Why is the original video file smaller than the compressed one?

Question

Video

Hello!
I am green in such matters, that's why I appeal. Help me to understand.
So I shot a video on mavic 2 pro, d-log, h.265 codec was used and 10 bit color.
So the original file weighs 3.5 giga - 5 minutes of video. (4k 30fps)
Turned it into a 30 second time lapse in Final Cut Pro (4k 30fps). If you output through ProRes 422 compression, then the file starts to weigh 5.5 gigabytes. And if you install Uncompressed 10bit - so all 50 gigabytes. Something is not clear to me, how can the source code weigh less than a compressed file reduced in time? Maybe I'm doing something wrong - I'm not good at editing.
The goal is to try to keep the quality and information from the original file completely, for later editing by other people.