It's to attract advertisers.

I imagine more and more Netflix properties will start to include product placement over time. I also expect a cheaper tier that's "ad-supported" sort of like what Hulu does.

Look at it from the flip-side. You, a classic theatre orientated studio, are looking for a distributer for your new film called 'Big Bangs & Car Chases', now you know that Netflix is a viable place to put your expensive film, if you don't want to go the theatre-first route.

Of course this all hinges on Netflix paying enough money for the rights that the lost cost of traditionally sold movie tickets is covered.