Could the 3rd-party apps allow users to config API keys? That would distribute the cost.
The cost is something like $500 per user per year. People just aren't going to pay that much.
From the data presented, in aggregate, >90% fall well within the free tier of usage (100 API calls per minute for OAuth logged in client). The majority of the remaining fall into a $1/month tier [1].
Certainly there are some outliers that exceed those ranges and unfortunately the majority of the spotlight seems to be on the smallest of the populace.
It is also worth noting that app developers can (and should) better optimize their apps to reduce calls to API (bundling, caching, etc) which will help to reduce the number of calls required overall to take that cost down. Many apps do this already.
[1]https://www.reddit.com/r/reddit/comments/145bram/addressing_...