> Companies like Qualcomm would have zero incentives to share their designs with anyone.

And yet, that's what linux did in 1991- they shared the code, lowering the cost of buying an operating system. I wouldn't say there is zero incentive, but it certainly lowers the incentive without a profitable complementary hardware implementation that can be sold for less than the proprietary isa when there is a royalty free license allows the manufacturer/fab designer "mask rights" to get a small margin within the difference of the foundry/ISA proprietary core competitor.