We don't currently have another way of enforcing this sort of thing, though, aside making software paid by default. How else will you convince a company that isn't even concerned with its long-term growth in favor of quarterly earnings reports to pay money for free software? Especially when you consider that (at least in the US) that sort of thing could get them sued by their shareholders.

Frequently threats of legal action, backed by the ability to follow through on them, are enough to get most companies to fold, and pay. I don't know that telemetry would be required in most cases, just because employees do talk, and usually publicly. I'm not sure if Unreal Engine does, but I can say with some certainty that WinRar didn't, and most of their money was made through commercial licenses on nagware