They did, but profit has always been a higher priority for them than market share and the 'platform dominance' that goes with it. If they happen to get a large market share, or if their platform becomes dominant anyway that's a nice benefit, but it's not a strategic goal.
A good example of when Apple became a market share elader is the iPod. If you look at Apple's product strategy though, they never did anything to gain market share at the cost of profits and premium branding. The combination of devices and services via iTunes created a dominant platform. They didn't do anything to avoid that, it's not that beign dominant is itself a bad thing, it's just that it wasn't a strategic goal. They never under-cut competitors to achieve it. Yet at the height of their market dominance, when they were best placed to use their position to exert market control, instead of using that power against customers to increase lock-in, they used it to force reluctant labels to embrace DRM free content. They then used it again to coerce the labels to sign up to iTunes Match. They did this becaue these moves ease customer pain points and improve the customer experience, making their products more attractive and therefore more valuable.
Can you imagine Microsoft or IBM making moves like that? I can't. As another example, Apple has always maintained that they don't allow third party keyboards, or third party browsers to use the accelerated Webkit engine for security reasons. These explanations were widely derided as fig leaves to cover a lock-in strategy, yet as soon as Apple has implemented controls to open these restrictions securely, it did so. It turns out their stated reasons for doing that really were their actual reasons for doing it. So if you want to make your 'Apple lockin would be worse than IBM' thesis stand up, you need to explain why their actual behaviour when they're in that situation doesn't match the thesis.