I have some sympathy for this. With the disasters of the WD 'Green' series and the recent revelations on how used disks were being sold for new. Synology doesn't want to be lumped with other companies problems.
They really have to sell it by minimising the price differential and reducing the lead time.
Slapping Synology stickers on Seagate drives doesn't make them magically immune from being mislabeled out of refurbishment.
This is the same old tired argument Apple made about iPhone screens - complain about inferior aftermarket parts while doing everything in their power to not make the original parts available anywhere but AASPs. Except here we have the literal same parts with only a difference in the firmware vendor string.
Honestly, you should just buy used enterprise drives. That they have hours on them is actually an upside, since most drives die either very early or very late into their expected lifespan. Our NAS is all Exos drives, no problems.
On the other hand, an NVMe drive from Crucial that lied about syncing data caused a write hole in ZFS and the associated pool broke to the point where we could only mount it with lots of flags in read only mode.
They really have to sell it by minimising the price differential and reducing the lead time.