The file size of exports has NO connection to the file size of the originals. If you thought it would, get rid of that thought.
Distance = Speed x Time. If you drive at 65 mph for 1 hour you will have traveled 65 miles.
Likewise the formula here is File Size = Bitrate x Duration. At 10 Mb/s for 10 seconds, you'll get a 100 Mb file.
So if you want smaller files, you will need a lower bitrate, a shorter duration, or both.
I think the only control we get over the bitrate of ProRes files is the flavor. Proxy will be lower than 422, which will be lower than 422 HQ, etc.