Really? It's a con that you can't get less than 512gb? If less storage was offered they'd just swap to "not enough storage in the base model." I can't take this seriously.
The cheapest 256 SATA SSD i can find is 15€. The cheapest 512 GB is 24€. That's a 9€ difference for double the capacity at retail prices. I can only imagine how marginal the cost savings for a big manufacturer like valve would be.
Why are you assuming that a cheaper lower storage version was possible? Cutting storage down further has effectively zero impact on their costs.
They started at lower storage a few years ago because they actually were pinching pennies to hit the price point and storage costs were higher. Now I can get a 2TB 5-7 GB/s drive (EDIT: the PS5 clocked it at 6600MB/s for what it's worth) for my PS5 for $100. Obviously that's not a direct indication of their costs, but I don't have those numbers and it does show how much the market has moved in the past few years. Their new base storage might not cost more than the emmc crap did on the launch 64GB deck.