I mean that's a common knowledge, no? if the cost of raw materials goes up, manufacturers hike up the prices of the final goods and consumers pay for it.
However when they announced both the pricing and the timeline, it's pretty clear that they are unreasonable. Apollo finding it unsustainable is just one developer and one app. Other developers tried to reach out to Reddit to actually sign up and get more information and they were ignored.
In principle, you are correct, this not a big deal. But in practice, it's been a total disaster. And didn't have to be that way -- they could have worked with their "partners" to ensure a win-win situation for everyone. Instead, they turned it into a lose-lose for everyone. They want control more than they want money.
Reddit would rather get rid of me than find a way for me to pay and I'd be happy to pay for it.
If Reddit does want to kill all third party apps complaining about how they haven't done a single thing to actually support 3rd party developers is kind of moot. But the point of the protest is how underhanded that is; they would be manipulating users and developers by lying about the whole thing. And if they actually didn't want to kill all third party apps then they still lied and are also incompetent.