- bash unix environment
- good user interface, better for personal use than Linux variants
- laptops had state-of-art hardware (though, not so much anymore) and excellent battery life (still the case)
- academic discounts
Of these, the bash unix environment is by far the most important for scientists. This means that they can write a program or script on their personal machine, and it will more or less behave the same way on the Unix computing resource. This is enormous -- and the main reason we put up with overpriced, non-expandable hardware from Apple.
If Microsoft wanted to sway millions of research academics away from Apple, they would need to ditch the DOS underpinnings that remain in Windows and switch to Unix conventions. I don't see this happening anytime soon, but at least Microsoft is no longer covertly trying to sue Linux into oblivion the way it was a decade ago.