Converting RAW NEF files to PNG/TIff - why is the converted PNG file 6x larger than the NEF file and TIFF 9x larger

I’m trying to convert NEF files to PNG or some other lossless format.

Using Preview/Imagemagick, the 10MB NEF file is converted to 60-70MB png file or 95MB tiff file.

Also tried converting to HEIC but it only allows 8bit depth, the resulting files are relatively small, 7MB.