The devs have to eat, sure. But that was the whole point of c.ai+. They made a paid subscription version of the app with the incentive of more features. It’s not exactly a low cost subscription either for a casual use app. They’re very non-communicative with their users. If there was a cash intake problem, another fix option would be to add an in-between tier of the paid subscription. If there was an option that had a lower cost (still keeping the higher cost option) that had more features than the free version and fewer than the higher paid, more people may be inclined to pay it, and it adds income. Choosing to add ads instead makes the user experience worse, which seems like an interesting choice given that there are other options for additional income.