> This makes it difficult to open source without open sourcing a bunch of hardware.

That's simply not true; there are many consumer-grade GPS clocks out there well within the bounds that spanner operates (iirc skew bounded at +- 5ms).

Not only that, but you can bet that if spanner were open-sourced, you'd see additional pressure to lower the cost of that hardware.

Not that the answer is any more nefarious: They don't open source it because it extensively uses google-only code, and open sourcing spanner would entail open sourcing many, many other parts of code, which is expensive. It'd be much easier to have something like the dynamo db local front to sqlite3 like amazon offers.