Most NVRs don't do AI (or even basic motion detection) --- they don't have nearly near the amount of processor power that a regular PC has. Usually motion detection, smarter motion detection (IVS for Dahua, Smart Events for Hikvision), and AI are done by the camera. The NVR basically just waits around for the camera to tell it that a motion/AI event is happening.
Since
Blue Iris runs on a PC, it has more processing capabilities and can watch the incoming video from the cameras and detect motion itself. It can also be triggered by the camera's built-in motion detection or IVS (tripwire, intrusion zones, etc). Or you set Blue Iris to do a combination of both.
What Blue Iris doesn't seem to be able to do is totally integrate with some of the cameras smarter features. For example, if you have a Dahua camera set to alert when a face is detected, Blue Iris can trigger an alert to notify you, but Blue Iris itself doesn't keep a copy of the face image in a separate location for you to go through and review later, like a Dahua NVR can. Same thing with Dahua cameras that have the built-in License Plate Readers.
What I didn't like about my Dahua NVR when I had it was that when I'd use the smartphone app to remotely check in to the NVR and see if there were any new alert recordings, it was cumbersome to use. I'd have to specify a start time/end time, and then it would show me everything that happened between those times. On the Blue Iris smartphone app, when you connect in remotely, it automatically shows you a thumbnail for all of the alerts that happened. I found that it a lot quicker and easier to use.
Both BI and Dahua's NVR can be viewed remotely, but you have to be smart about how you set that up. Setting up a VPN is recommended no matter which device you ultimately end up choosing. Both the NVR and BI have smartphone apps that can be used to view remotely, as well as built-in web servers. I don't know if this has changed, but at one point the Dahua NVR required a browser plugin if you wanted to use the web server. Blue Iris doesn't. That was one less level of hassle to go through.