Zero and minimal are the same thing when it costs non-minimal resources to bring something to market and reach potential customers through advertising etc. When it costs you $15 to make a $10 sale you are not losing money to abandon the market.

The test doesn't require there to be no impact on the commercial viability of the work; rather, benefits exceeding the loss in commercial value of the work is one (important) factor arguing in favor of fair use.

If there is value to them, why are the copyright owners not offering a way to pay them?

Be interesting to know if Sony et al are selling these songs (as MP3s, rather than 78s, I'd assume) and if so how much they make. That would presumably be used to judge the actual commercial value. And this would only apply to the songs which are still in copyright - sadly not zero given they're all by definition at least 70 years old.