Beyond initial development costs, it didn't cost Valve anything to ship the Index with Alyx though. Bundling in a $200 voucher would be increasing the system price by $160 in direct cost to Valve for no reason, as consumers are likely to spend that after purchasing the system, but might be dissuaded by a high initial purchase price.
A more apt comparison in that scenario would be Valve bundling their entire software library with the Steam Machine, or developing a new game to bundle with it as a means of adding value.
They don't seem to be particularly concerned about supporting the Russian war machine.