Violating OSS licenses is far more common with e.g. desktop Windows software than with Web-based SaaS.
At least with native code I can check what is on my hard disk.
And given my experience, it is hardly the case any company outside the big SV ones or whose main business is unrelated to software, that actually bothers to contribute anything back.
And there is no way to validate that.
while i agree with your point about this being sub-optimal for both software-development and free software as a whole, i think it is a separate issue.