It depends on the HW:SW cost ratio and the volume. In favourable case the extra bit on the price tag can amount to a rounding error. Moreover, the price tag includes a profit margin, which is usually adjusted to match the competition already.
Besides, "ignorant" HN comments on e.g. FOSS software and funding problems have mentioned that the paperwork you have to do to buy software licences can be a PITA, so free software can be perceived as a plus when the R&D selects the parts.
People have already thought of that, sure. But has it been thought about and executed properly? Like the added value of open-sourcing the SW (made a lot easier when you don't need to copy-protect it). Or do they just go for the extra source of profit the SW licence sales provides, anyway?