Ok, let's do the math:

Say app has 10MiB, 100,000 downloads is ~1TiB, 1 have a 1GiB/20GiB VPS with that monthly bandwidth which I pay $1/month.

So distributing 100,000 copies costs $1.

I'll give Google $1 for distribution of 100000 copies of my app. Fair?

Yeah, I'll give Google a bit more for payment processing, perhaps. But actual distribution costs nothing really, for most apps.

Remember that creating a Google Play account already costs $20, so for the most people the distribution costs are far more than covered.

you completely ignore the #1 cost: human cost to setup your vps, manage it, backups and whatnot etc. you gotta take all costs into account.

not every developer is willing to learn and spend time configuring & managing a server. that's not the same skill set.

Human cost is not really very well measurable.

First we're talking about the free app for a good cause, so you're already providing an app for free, so you've assumed some sacrifice for others for whatever reason, and setting up a website for it may be comparatively negligible part of the whole cost to you in terms of time.

In my case I would have already had an infrastructure and knowledge how to host things, so it might take a few minutes to put some new files up on a machine used for other projects. Additional costs being pretty much 0.

And there may be benefits (even if I didn't have the knowledge and infra) like learning something new, or now having an infrastructure and knowledge that helps you save expenses or time in the future. So that would offset the costs. You can't just look at costs alone.

Google also does the work of keeping fake versions of your app out of the store.

I remember that being a problem in the app store for windows phones. Lots of fake apps that used the VLC name and logo, for example.

Android is worth sh*t without any apps. I consider providing a market for apps and managing the quality of the market is their responsibility, business expense not developers.

If they don't like free apps, then they should stop hosting free apps if they want that 30% tax so much.

Google should be thankful in the first place that developers are making apps on their ecosystem (doubly so for open source apps), because without them, Android and the Google Play Store itself isn't worth much. It's their part of the deal to stay relevant.