there's still a fairly lucrative parts stripping market and there are extreme efforts that are used to "unlock" locked devices - it has been known in the Chinese marketplace that you could get paired chips to do SMD rework with a "clean" set of identifiers. they'll swap the SOC, the flash, and the wireless all for a few bucks.
replyolder iOS devices as well are also vulnerable to having their syscfg rewritten via exploits, so you can "clean" a locked device that way as well with a good set of serials. Apple Watches are a hot one for this.
On top of that a sizable percentage of theft victims don't even bother to report it stolen.
replyYou can't activate the hardware with a different ID regardless. It requires the owner to relinquish ownership.
replyI'm sure this is different with different components of course depending on how granularly apple tracks their hardware—but the whole package certainly can't be activated.