Because FFmpeg respects the source. When you use -c copy , you aren't re-compressing the episode. You are telling your computer: "Hey, just copy the bytes from 5:23 to 6:45 exactly as they are."
Sitcoms like Abbott Elementary often have high static backgrounds and dialogue-heavy audio, which compresses very efficiently. If the file is too large, you can reduce the file size significantly using H.265 (HEVC).
ffmpeg -i "Abbott.Elementary.S02E02.1080p.mkv" \ -ss 00:05:23 -to 00:06:45 \ -c copy \ "abbott_s02e02_gregory_eyeroll.mkv"
