As a long time user of Windows which historically had an incomparably large amount of security incidents, I can assure you that Apple won't get blamed that much for 3rd party data breach unless it involves Apple's own service and user data.
I’m talking about the general public. If a story about a data breach in a 3rd party app — affecting iOS users — hits the news cycle, Apple will take the blame and their brand reputation and sales will be impacted. It doesn’t matter whose fault it really is, Apple is the face of the iPhone and through their walled garden they have accepted final responsibility for everything that occurs on iOS.
You can draw a direct line between Apple’s original marketing pitch (easy to use, simple, secure, appliance-style computing) and the iOS walled garden. Just as you can with Disney and their family-oriented brand. It’s not a compelling argument to say that other film studios have nudity in their films when Disney is the brand at issue.
They didn't take security seriously when they were laying down the architecture for Windows because they didn't think they had to. Apple is taking the exact opposite approach. They're fairly obsessed with security and privacy because that's one of the big selling points for the whole iOS ecosystem. They miss things because they (like us) live in the real world but they do pay a lot of attention to it and the number of updates for things like 0day defects that arrive within days of the defects being reported tells me that this continues to this day.
Apple doesn't have a monopoly. Per https://gs.statcounter.com/os-market-share/mobile/worldwide Android has twice the market share that iOS has. The reason for all of this generated drama is found in https://www.businessofapps.com/data/app-revenues/. The key bullet points are:
"App Revenue Key Statistics
* Mobile ad spend in 2022 reached $362 billion, a 7.7% increase on the previous year * Android and iOS app consumer spending increased to $135 billion in 2023 * iOS was responsible for 66% of app consumer spending in 2023 * Games accounted for 60% of consumer app spending in 2023. Google Play contributed 41% of the total amount * Subscription revenues increased to $45.6 billion in 2023, iOS was responsible for 76% of that revenue"
The real reason for all this foolishness can be found in these bullet points. 66% of $135 billion is $89.1 billion, and lots of people would love to get a piece of that pie without dealing with Apple (who built and owns the stack). It isn't a monopoly, though, and all of that monopoly talk is misdirection.