The cost of "security"

[tellurium]

Possibly because the datasheet seems to be only available under NDA.

Yep. It is not an issue to get it though, but unfortunately all secure element vendors I know, require NDA.
Maybe that's a regulations thing.

[Nominal Animal]

The Microchip team that develops ATECC608 did a significant job in promoting it

Perhaps to the hardware folks, but definitely not to the software development side; not even to Linux kernel folks (which is, no matter how you look at it, a huge part of the embedded networked device world).  Neither linux-kernel nor openwrt-devel mailing lists have a single mention of the chip, for example.

Possibly because the datasheet seems to be only available under NDA.

Aw crap.  I missed that, even though it is highlighted in orange at the top of the datasheet.

On the other hand, the interface library to the chip is available at github, so I don't think Microchip is per se hostile to open source and developers like myself; it wouldn't be the first NDA I've signed (and scrupulously followed).

(As to the license stating "exclusively with Microchip products", it does not say "with exclusively Microchip products".  The library itself makes that clear, by stating that it "is structured to support portability to ... multiple environments including bare-metal, RTOS, and Windows/Linux/macOS".)

Yes, I too believe this NDA is some export control thing.

[peter-h]

The chinese always get these "confidential" data sheets immediately. See this thread for example
https://www.eevblog.com/forum/embedded-computing/sd-card-proprietary-modes-have-these-escaped-into-the-wild/msg3781682/#msg3781682