It's not specific to open source but it's most clearly enforceable with open source as there will be many contributors from many jurisdictions with the one unifying factor being they all made their copyright available under the same license terms.

With proprietary or more importantly single-owner code, it's far easier for this to end up in a settlement rather than being drug out into an actual ruling, enforcement action, and establishment of precedence.

That's the key detail. It's not specific to GPL or open source but if you want to see these orgs held to account and some precedence established, focusing on GPL and FOSS licensed code is the clearest path to that.