Rooted users started noticing the app gone from Google Play on their devices over the weekend, and Netflix eventually confirmed it did this intentionally. The streaming service is now using Google's Wildvine DRM to block the app from rooted devices that don't pass Wildvine's security status, and its Google Play listing will not appear for devices that fail a SafetyNet check, which not only rules out rooted phones but also unrooted phones that are bootloader-unlocked.
Netflix has long been wary of the Android platform over root and piracy concerns, so much so that it took years for the service to come to Android at all. Blocking rooted devices makes a certain amount of sense from its point of view, even if the vast majority of root users aren't using it for anything nefarious, but blocking phones simply because the bootloader is unlocked is going to cause a lot of headaches. Unlocking the bootloader on a phone will cause it to fail the SafetyNet check for Google Play, even if the phone's software hasn't actually been modified, and can be needed for processes like flashing sideloaded updates and even flashing the Android O Developer Preview.
There are ways around this, but it's also worth mentioning that root on the whole is far less necessary to the Android experience as it was years ago. Phones are more full-featured, even allowing users to theme their nav bar and alter the system UI nowadays if you buy the right phone. Wi-Fi tethering is offered out of the box on most phones — though yes, your carrier might charge extra for tethering.
If you've got enough reason to root, Netflix playing hard-to-get probably isn't going to stop you any more than the laundry list of other apps that don't play nice with it. That Netflix isn't playing nice with bootloader-unlocked phones that aren't rooted is slightly more dismaying, especially as a summer of Android O betas to sideload and test awaits us.