Google and Microsoft are the kings of multi-billion dollar acquisitions (which generally end up a waste of money). Apple rarely drops more than a hundred million on an acquisition and when they do, it's for a foundational technology. Even PA Semi which is the foundation of their chip architecture was a sub-billion dollar acquisition.

Notably, their two big $1B+ acquisitions were Beats and Next.

Alternatively, Apple could not buy them and save the money. Less flippantly, while Apple seems to be heavily invested in AR, they're... well, already heavily invested in AR. There would need to be a compelling argument that buying Magic Leap would jump them farther ahead than they could get on their own.