(I'm saying this with my CMU hat, not my Google hat.)
The era of the mainframe, with each provider competing with a custom chip, wasn't necessarily beneficial for individual buying computer power.
If you look at processors, you see that with the early custom processors, followed by some standardization and copy around the IBM S/360, followed by more proprietary innovation around the PC era, resulting finally in the x86, eventually disrupted by the mobile chips, which then consolidated around ARM and so on.
With cloud computing, we are essentially going back to the era of time-shared mainframes with remote access.
The (expensive) report from The Information upon which that article was based speculates a little more about chips for training.
For a while, it's very likely that Google will be the main user of these, so there's still plenty of incentive for it to increase efficiency and reduce costs.
It may be that the other cloud providers would then sell them to those individuals. Indeed, the job of entities called "distributors" to buy big lots from manufacturers and break them up.
And of course, I don't know what the point of (apparently) keeping them out of the average person's hand would be.
It makes any benchmarks become Google-cloud benchmarks, right?
Edit: I am complaining a bit about the lack of availability but there's also a real point here. If there's no source for TPUs outside of Google, Google Cloud competes only with other cloud providers and with owning physical GPUs - long term, it has no incentive to be anything but little bit more efficient than these however much it's price for producing TPUs declines.