I can definitely think of a reason.

Direct access to all Netflix subscribers.

That database is extremely valuable.

The number of subscriptions isn't very high (for companies like Microsoft, Apple, and Google), but these are paying households, 220 million of them.

And people in those households interact with Netflix daily, or at least a few times a week.

Business users are also consumers. Plus Microsoft has a long history of targeting students. Get them when they are young.

I would offer a bundle with Netflix and an MS product and use that MS product to try to convince customers to upgrade to an MS Office subscription or an Xbox pass.

I can see a low-res, one screen only subscription, very cheap, with MS adds for emerging markets being very effective.