Yep. They're too slow to be useful running 10.11 or 10.12, especially with HDDs.
They're not worth the time/effort to modernize from a business perspective, so into the recycling/donation bin they go.
Or course that doesn't prevent the user for doing any updating if they're so inclined.
And I don't know what ones actual description of "slow" actually is, but my older 2007 2.2GHz MBPro does quite well for normal stuff and running El Cap'n OS X 10.11.6, and yes it does have an SSD installed, and it's SATA bus is only 1.5Gbps.
But I'll bet there are still a lot of youngsters and low income families fairly close by that would probably enjoy receiving an older "slow" Mac, and as you say, they don't have much in the way of resale value.
And heck, even a replacement 7,200RPM 2.5" HDD can do wonders to speed things up for even less expenditure vs SSDs.
All you'll need is a sketchy van with a recycler logo on it. Back it up to shipping on the right day and you're in luck!
Kidding aside, you won't get a thing (on the up and up.) Where I work, there are only two ways an asset leaves the service of the company; recycling or warranty replacement. And in both cases, the drives are shredded before the unit leaves.