Simple The Best Picture Winner could win because it had a better story for example making it a better overall picture while the Best Director did a better job actually directing their movie.
Keep in mind that Netflix does sometimes release original content on disc. Both seasons of Stranger Things for example has been released on DVD, Blu-Ray, and UHD Blu-Ray.
Regal is being very sneaky about this year's festival:
Enjoy all of the year’s best that played at Regal with the 2019 Regal Best Picture Film Festival! Come out to select Regal locations between Friday, February 15 and Sunday, February 24 to experience the best that 2019 had to offer...
I can see people who attend all of the AMC and Regal Best Picture series screenings being confused as to why they didn't see the movie that wins Best Picture.
If it gets a best picture nomination it will probably come to a lot more theaters. Regal for instance has a program where they rotate every best picture nominated film for a week for a reasonably small subscription fee.