How tough is writing a quantitative methodology chapter of thesis?

Dear Admin! I have read many threads here. It’s glad that here many people find the solutions to their problems and it is really motivating that PhDs share their stressful (perhaps many aren’t stressed at all) experiences here and somehow finds support with the interaction.
Anyways, can someone help me to find out why I’m not able to write my methodology chapter! Like seriously! I freak out every time the research methodology chapter lying on my study bench and with a stamp of REJECTED. I have written this petty little paper almost 7 times but still the comments of my supervisor are same- This piece cannot convince me why you chose quantitative approach, why collected the data through interviews and not from the existing documents, why only SAS is used and not SPSS. He needs more! More elaboration, more strong arguments, more peculiarity! But it is just a methodology chapter okay? What more clarity does he need?