I did this for a while, but there are some features of things like Jellyfin that attracted me and I've gotten value out of. A major one is maintaining a record of your progress. Depending on your viewing habits, including how many devices you may use, as well as other aspects, this can be very useful. For example: watching a video on a desktop computer in one room and resuming its playback in another room.

What about users accounts to the share the files and then adminstrating those users over the internet, what about metadata and images for browsing. What about viewing on Smart TVs. Plex and jellyfin offer a lot of functionality that your suggestion wouldn't account for so I don't think anyone has forgotten they just find a personal Netflix to share with family and friends very useful.

hmm, I wonder if there's any value on top of that functionality that Plex provides?