Why RGB print file does not print well on offset as per expectations?

RGB colors are strictly of online/onscreen purpose. Offset printers use plates, where each plate prints an individual color (CMYK + any additional spot colors). RGB colors when ripped will change the color codes and give you an unpredictable result, thus your output will not be the same anymore.

RGB colors are made for Digital use ( web, mobile, motion graphics...) but it's not for printing. The printer doesn't understand RGB color mode.

in this case you have to use CMYK color mode in order to get the exact colors, the printers are made to mix the CMYK ( cyan magenta yelllow K-Black) colors to give you the perfect result with a300 pixels per inch resolution.

I like your answer and also raising new question for you :)