They are commercializing the silicon, by selling access to it on their clouds.
Now, I know that what you actually mean is selling the chips themselves to third parties :) But it's not obvious that there's any point to it given their already existing model of commercializing the chips.
First, literally everyone is already supply-constrained due to limits on high end foundry capacity. Nvidia has a ton of capacity because they're one of TSMC's top two customers. The big tech companies will have much smaller allocations which are used up just supplying their own clouds. Even if the demand for buying these chips rather than renting were there, they just don't have the chips to sell without losing out on the customers who want to rent capacity.
Second, the chips by themselves are probably not all that useful. A lot of the benefit is coming from the silicon/system/software co-design. (E.g. the TPUv4 papers spent as much attention on the optical interconnect as the chips). Selling just chips or accelerator cards wouldn't do much good to any customers. Nor can they just trust that systems integrators could buy the cards and build good systems to house them in. They need to sell and support massive large scale custom systems to third parties. That's not a core competency for any of them, it'll take years to build up that org if you start now. And it means they need to ship the software to the customers, it can't continue being the secret sauce any more.
Nvidia on the other hand has been building up an ecosystem and organization for exactly this for the last decade.