Why is this $50 less that the other 6TB IronWolf Pro drive on Newegg's website?

Because its used. It is not clear in the advertising. A fake word for used is "Renewed" or "Refurbished" Only in the fine print comparing to similar products does it show REFURBISHED.

Questions & Answers: Refurbished: Seagate IronWolf Pro 6TB SATA 6Gb/s 7200RPM 256MB Cache 3.5" Enterprise NAS Server CMR HDD

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Seagate IronWolf Pro 6TB SATA 6Gb/s 7200RPM 256MB Cache 3.5" Enterprise NAS Server CMR HDD — ST6000NE000

Optimized for NAS with AgileArray
Actively protect your NAS with IronWolf Health Management
High performance means no lag time
Rotational Vibration (RV) sensors
Do more in multi-user environments
Designed for always-on, always-accessible 24×7 performance
Retail or OEM packing may vary

$379^.99 –