They are paying for the brand, not the product. Microsoft is ensuring that they have mindshare in the next generation of gamers. That's critically important to maintaining their ongoing success in the gaming sector.
Similar to why Disney paid billions for Star Wars: the company was easily capable of replicating the product; the issue was replicating the brand. That brand has a proven track record of multi-generational appeal.
I think it's more than just the brand right? I can't speak for Disney and Star Wars because Star Wars was never my thing.
These creative endeavours have a soul, or an essence, for want of a better term. You can replicate a game or a movie and it will feel utterly soulless compared to the original, even if you can't visibly notice a difference.
You could reproduce Minecraft but even the most infinitesimal divergence from the original will make it feel fake. Maybe the controls have a different 'feel', or the way the scene is rendered feels a bit off. It's just not Minecraft any more. There are just so many quirks and details that will be lost in the translation, or even patched over if they're seen as bugs.
It's no different if you ported a game from Unity to Unreal and then to CryEngine. I'm sure that with a blind comparison you would be able to 'feel' the difference.
And the same for films. The way these things were created has a lot of influence over the end result.
On the other hand, it's exactly what can make a remake or remaster so successful. The Resident Evil 2 and 3 remakes that followed Resi 7 were phenomenal! Not totally faithful to the originals, didn't try to be...they just took an older game and gave it a new life.
People don't go to Starbucks because it's the best, they go to Starbucks because mocha frappucinos in Lima and London taste exactly the same. Any divergence, even an infinitesimal one, makes the frap feel fake.
Sure, marketing is important. But the "secret" ingredient is coca leaf extract. The actual cocaine is used to make various drugs by a different corporation.
According to Business Insider, the beverage company has a deal with the Drug Enforcement Administration to get coca leaves so that the world can get its Coca-Cola fix. The DEA lets Coca-Cola import coca leaves from Peru and Bolivia in order to get the part of its secret recipe, which it hides behind the term "natural flavors" on the ingredients list.
Which can be done, but it is a long process. Most attempts only get a fraction of the big brand, and the exceptions generally have more to do with the failings of the big brand than the competition. Once people find something they like, as long as that thing doesn't do something stupid they won't be in a hurry to look at the competition in general. If there is any switching cost they are even less interested in trying something else. Which means that the not number one competitors need to be perfect in everything - which is hard when they are not getting as much revenue to begin with, and thus cannot afford to try out any seemingly good ideas that turn out bad only after you try them...
Similar to why Disney paid billions for Star Wars: the company was easily capable of replicating the product; the issue was replicating the brand. That brand has a proven track record of multi-generational appeal.