I'm not the one you asked, but I think the underlying issue is that the Unix security model is built around the assumption that software shares the user's intent, and is treated as exactly as trusted as the user. Computers at the time tended to be multi-user, so the focus was on protecting users from other users. While there was a risk of overtly malicious software, preventing remote code execution attacks and teaching users not to run trojan horses was mostly sufficient (for Unix users; the broader population using Windows often installed malicious adware in the early 2000s).

In a modern environment, software should not necessarily be trusted to act in accordance with the user's wishes or best interests, and there's often a financial incentive for software creators to do things users wouldn't want them to. In the early 2000s, the most visible issue was Windows software that displayed advertisements outside of the software, often not obviously connected to the software. It would often monitor the user's browsing habits and such, leading to the name "spyware".

Spyware of that sort was universally considered malicious, but modern smartphone apps often send far more sensitive information, such as location and address books to their creators. Those provide a simple example of a situation the classic Unix security model doesn't address very well. I am the only user of my phone, and I obviously want to be able to read my address book and get my location from the GPS. I do not want the latest and greatest app for sharing pictures of my lunch to track my location to show me restaurant ads, and I only want it to know about people I have explicitly connected to within the app, not my whole address book.

Android's security model addresses that to a degree, restricting some capabilities until the user explicitly allows them. Some of these, like filesystem access aren't handled very gracefully, and it's possible for an app to refuse to work until granted permissions it doesn't really need (this is against policy for inclusion in the Play store, but enforcement is imperfect, and software can be installed from other sources). One workaround seen in XPrivacy is to feed fake data to apps.