Because you get to dictate how you watch the content; You don't have to deal with enshitified or just straight garbage apps from the streaming source; and finally, you can keep it for posterity indefinitely if the mood strikes you.

I maintain my own media server and it's such an infinitely better experience than anything currently out there.

You don't have to deal with hopping between the garbage Netflix app, and the garbage Prime app, and the garbage Disney app, and...