One theory is that they already have the components to build them purchased. They may also have a contract with the factory to build 'X' number of devices, in order to have achieved a discounter labor rate, etc.

So, HP has a sunk cost in components in stock, and an obligation to the factory to build more units (or else pay a penalty).

Is it then cheaper or even slightly more profitable for them to build more tablets rather than try to dispose of the parts and deal with broken contract issues.

(my theory)