The problem they had was that they sold individual standalone products, not platforms. There was very little to keep a user with the same vendor other than liking the next product. A platform is a different beast completely, and once a platform or set of platforms gets established at scale in a market, it’s almost impossible for a new entrant to compete with it.
This is because platforms have three advantages. The first is a user’s sunk investment. I own hundreds of pounds worth of iOS software, and even the free software I use took an investment of time and effort to learn. Plus I now have considerable assets in those file formats and storage systems. Switching to a new platform would be expensive in money and time. The second advantage is network effects, my whole family is on the same platform, so is my company and many of my friends using the same services. The third advantage is the ecosystem. There is a plethora of software and services available for iOS that a new entrant won’t have, many offered by third parties. In competing with iOS and Android you’re not just competing with Apple and Google, but also the entire ecosystems of companies that complement them. These three advantages also apply to Android and its users.
This is why even Microsoft could not break into the modern mobile smartphone platforms market, they were too late. Android and iOS had critical mass in all three areas. Google was incredibly lucky they managed to get Android up to being a viable platform before Apple had the entire mobile platform market sewn up. Fortunately the Android team at the time knew the new game they were playing when they saw the iPhone announcement, and realised they were in a race against time for survival.
This is also why the desktop is dominated today by the same platforms it was in the 90s. Mac and Windows. Arguably we could extend that to the 80s with Mac and DOS. That’s around 3 decades of stability. The mobile market in its current form was established around 12 years ago. I would not be at all surprised if the mobile market is still dominated by Android and iOS in another 20 years. There are incredibly powerful forces driving this.