It probably depends on the criteria. Is this the biggest West Coast relatively sexy tech employers or is it the large-ish companies with the highest average comp for a given level of software engineer? (I actually agree that, in general, Microsoft probably belongs on the list more than Netflix does.)
The term FANG (and FAANG) was coined and popularized by stock market investors, not tech workers/job hunters. So it's about the highest growth large-cap tech stocks, not the absolute largest market caps or most well-paid/prestigious jobs.
It was coined in the Ballmer days, when MSFT's stock price had been stagnant for about a decade, so no surprise that it got left out. Things are different today though.
Netflix doesn't come close to matching Microsoft or the others.