I think the main concern for the people wanting to stop this isn't people wanting to print things for personal use or non-profit organisations, it's that for-profit organisations/businesses will use your work for their own profit. And this bill will make it easier for them. As an illustrator, if you don't register your work in one of these private, for-profit registries, it will be legally orphaned, and is then available for commercial infringement by “good faith” infringers. Good faith infringers would be anyone who believed they had made a “reasonably diligent,” but unsuccessful effort to find you.
And this is of course where a lot of debate could take place. Today you can't use something you find online and use it for profit even if you can't find the owner. This bill opens up for that. And that's why they expect there will be a need for a Copyright Small Claims Court. It's because they expect there to be a flood of orphan works lawsuits. It doesn't matter if it's for the benefit of illustrators/artists. They just expect there to be so many as a result of passing this bill, because there WILL be instances where companies use work that belongs to an artist.
I don't know everything either! And maybe the actually passing of this bill won't have a lot of effect "in real life", but it's better to have the law on your side, and this is a matter of principle. Again, the fact that they've tried to pass this bill for so long is because they see a lot of profit in it (not for artists), and there's a reason artist organisations are against it.