Could you tell me what your company is and/or what category they are in where they are making this much a day? I can understand gaming as they are very popular, I heard candy crush during at their peak was bringing in that much.
It is still generally harder to make serious money from apps but possible.
Also, games are very different than Apps. People are more willing to spend money on entertainment than apps. Some exceptions are dating, health, finance though.
Back in 2014 and 2015, I launched an app on windows phone and android respectively. They both made a few thousand within a couple of months. I discontinued them, but mostly because the competition on Android was too much and I was unsure about the product strategy going forward. Fast-forward years later, and several of those competitors also shut down, leaving room for other apps in that space to grow and take more marketshare. I really think you have to just keep at it.
I actually think Apps were difficult to make money from years ago but that was because several factors such as competition, consumer spending habits, lack of incentives from iOS/play stores.
Now, I think things are a bit different:
1. Fewer apps as the tech sector has shifted to more cutting edge tech like crypto, etc.
2. Quality of apps have gone up
3. In-App purchases are very common as are Subscription models
4. People are more willing to spend on IAP and have gotten used to subscriptions
5. Stores have reduced taxes to %15 in some cases
6. People are using fewer apps these days, no more app explosion.
But basically, you're app has to be high-quality and useful. Also, the main drivers for app installs are still the app stores themselves, so you have to optimize for the app store. Look into ASO ( app store optimization ). Also, expect to take a long-time to build up your audience. I'm attempting to launch a new app now, and going through this process.
Regarding ios vs android, it's easier to make revenue on iOS for sure, but again, if your app is high-quality and useful i'm not sure it makes a big difference.