A lot of companies want to support projects without advertising that fact. Sony spent a seven-digit amount on open source software while doing things like contributing code via shell companies in order to avoid revealing what tools they were building their products around. I've received more than one email saying "this patch fixes a bug PLEASE DON'T TELL ANYONE IT CAME FROM ME".
Amazon has chosen for some reason to avoid advertising their open source contributions, but they absolutely do make contributions. Would it be nice if they contributed more? Sure. But that's true of every company.
If the goal however is to get companies to contribute more then the simultaneous applauding/shaming of a public donations registry is likely to encourage some companies to contribute because they like to be seen as good corporate citizens and not poor corporate citizens.
I can imagine for some companies it would be a matter of corporate pride to advertise their "projects financially supported" page, perhaps even as part of their recruiting effort to advertise how developer-centric they are.
github is the logical home for this, and indeed it is in the interests of github to do it - open source projects are far more likely to want to host on github if it has a public donations registry that, due to its public nature, actually works.
Is it really good idea to give github defacto monopoly power? This would make it much harder for github competitor to arise and business competition is a good thing.
Especially since as politics and culture tend to be more and more polarized, you don't want one company with that much power.
On the other hand, imagine if it really worked and money poured in to support open source projects - it would be transformative for the lives of many open source developers.
Github did populist political decisions in the past. They will move from "united meritocracy of Github" to full sjw and back in blink of eye.
They do a lot of good for open source, but I would not trust them not to close project due to political reasons - especially under pressure. They are not the pick of a company I would do for project that aims to "shame" companies/individuals when they misbehave.
Amazon has chosen for some reason to avoid advertising their open source contributions, but they absolutely do make contributions. Would it be nice if they contributed more? Sure. But that's true of every company.