If we the people as represented by our government decide that a particular foreign regime is off-limits, then companies are compelled to not do business with them. We don't leave it to choice.
So if you want companies to have any form of morality, you need to enforce it. Because otherwise all the ones that do care are just going to be outcompeted and die out, and you'll be left with specifically the worst of the bunch. Organizations and individuals act to their incentives, and if they don't, then they stop existing.
If ethics were self-enforcing, then we wouldn't need to be talking about it. We have laws against killing and stealing because without those laws, killing and stealing are a shockingly effective way to get ahead.