See this 8y old thread about what EA does on Android: https://old.reddit.com/r/OutOfTheLoop/comments/3mikbc/whats_...
(Too late to edit)
Partner wanted to play all the time. I discovered the videos ads were using up all of my prepaid data before the end of each month. I bought the premium version, which was a one-time purchase "back then".
They launched an app revision that had a handful of very noticeable bugs. Then they changed to a new app (rather than upgrade), pushed all the users to the new app, and made the ad-free version a subscription. What do you get for your monthly payment? Well, nothing significant, like you'd expect from a subscription.
In fact, they essentially crowd-sourced their Q&A content by letting users submit feedback when a pair was inaccurate, so users are fixing problems in the content for free.
Server usage?
Not to minimize the daily work of countless devs, but a quiz game is essentially a handful of databases, a dollop of quite straightforward logic, some static UI visuals, and then content scraping to fill the main Q&A database. The logic and UI visuals almost never need a rewrite. DynamoDB is pennies per month per user, and if you're a real POS you can use long advertisements to push away users temporarily when your RCUs/WCUs are getting close to a scale-up threshold, which has the nice side effect of increasing revenue if everyone watches the long adverts anyway.
I guess they expected a percentage of users to bail switching to subscription, and that doesn't cost them a cent. You said it best: shady
There are IAPs to unlock brushes and other things, and a small fee to buy everything. I believe I paid $15 one-time to get everything for Infinite Painter.
The problem with allowing IAP to be used for a shareware-like unlock is that there's nothing stopping shady developers from forcing a subscription on you later even though you already paid now. Forgot which one that was, but this kind of double dipping recently happened to a popular baby monitor.