Microsoft just unveiled Office for iPad. The move makes complete sense. The iPad, after all, is by far the strongest and most popular tablet platform on the market today (although Android has been rising fast). Any software developer, including Microsoft, wants to offer an iPad version of their app.

So what took so long? Apple unveiled the iPad way back in January 2010 — more than four years ago. By summer that year, it was clear Apple had yet another hit on its hands, single-handedly creating the mass-market tablet category that every other hardware manufacturer was soon racing to enter.

The man behind Office for iPad said he was thinking about how Office would work on the tablet as soon as it was unveiled. Virtually every Office competitor, including Google, launched native apps for creating and editing documents on the iPad over the last four years. Microsoft appeared to be on the verge of launching Office for iPad back in 2012, but the rumored launch failed to happen. Former CEO Steve Ballmer later confirmed Microsoft was working on an iPad version, but that it was waiting for the touch-friendly version for Windows.

As it turned out, the iPad version came first, which, in light of Ballmer's comments, suggests it could have debuted even earlier. To understand why Microsoft waited so long to pull the trigger on Office for iPad, you have to understand the culture of Microsoft, and the company's strategy surrounding Windows 8.

Office's Ride Through Windows

Microsoft debuted Windows 8, which adapted Windows for the touch-first environment of tablets, in September 2012. A key part of the rollout was the Surface RT and other Windows RT devices. Microsoft gave every Windows RT device a free version of Office in an attempt to kick-start its tablet platform.

Development for Windows 8 began years before the launch — before the iPad launch, even. Long before anyone had heard of a Smart Cover, Microsoft was already hard at work on its tablet OS, and a strategy was taking shape. Microsoft announced it was building a version of Windows to run on ARM-based devices (like tablets) in January 2011, which eventually became Windows RT.

Because Windows had to be re-coded from the ground up to run on ARM processors, it was clear that apps made to run on older versions of Windows wouldn't work on Windows RT machines. That means no Quicken, no Acrobat, no Office. Windows RT tablets would run the new, touch-first apps only.

Problem: There weren't any new touch-first apps yet, and there probably would be very few at launch. To boost interest in its budding tablet platform, Microsoft decided to make Office the free toy in the Windows RT happy meal. Every Surface and Windows RT device would ship with the suite pre-installed.

At the same time, the Office team was building Office for iPad, it appears. Remember: Microsoft is a sprawling company, with many different divisions. While Steve Ballmer and Steven Sinofsky (neither of whom are with the company anymore) crafted the company's Windows 8 rollout, Office was slowly adopting a strategy that would see its apps spread to more platforms. OneNote, notably, came to the iPhone in early 2011.

However, a version of Office for the iPad, if launched before Windows 8, would have undermined the entire strategy behind the Surface and Windows RT. The fact that Windows RT devices gave buyers a "free" version of Office was their primary selling point, supposedly making up for the lack of support for legacy Windows apps. If the most popular tablet in the world already had Office, why would anyone buy a Surface?

Bye-Bye, Windows RT

Of course, things didn't work out so well for Windows RT. It turned out no one wanted to buy Windows RT tablets anyway, and every Windows manufacturing partner (except Nokia) has given up on the platform. It didn't help that the full Office 365 rollout didn't happen until months after the Surface launched, but it seems Windows RT was a dud with consumers, whether it had Office or not.

Also, with Ballmer being succeeded by Satya Nadella — a man who's been drinking the cloud Kool-Aid for more than a decade — any lingering cultural reluctance to open Office to more platforms was cast aside. As he made clear from today's event, Microsoft's strategy is Office everywhere — on every kind of device, from phones to PCs and everything in between.

Which led us to today. Office for iPad has probably been more or less ready for a while, but Nadella likely gave it the final push, countermanding Ballmer's assertion that the touch Windows version would come first.

Notably, there are serious technical challenges in creating touch Office (the Windows version connects to apps in a fundamentally different way than Windows 8's "contracts," for example), so it's very possible the Metro/Modern version of Office needs more shakedown before its official debut, even though Microsoft teased it about a year ago.

Office for iPad was ready, and with the de facto failure of Windows RT (there are really only two major products that still run the OS), Nadella saw no reason to hold it up any longer. If this launch confirms anything, it's that trying to use Office as "special sauce" for Windows was a colossal mistake. In his first public act as CEO, Nadella has corrected that mistake.