In my opinion the abandoned demo was good for many reasons, so here are the reasons

1. It showed the most content out of the demos- you see the other eras usually just showed the gameplay of the floor 1, (excluding the remastered era because it had no gameplay) The abandoned demo was an exception, after you complete the demo, you get small sneak peeks of other content, this includes G.P.D mode, and a small preview of what the extras menu would look like.

2. Animatronics actually attack you, now the abandoned demo floor 1 is the same as the rebooted era, but with the addition of lockjaw hunting you down, now I’m aware the unfinished demo had Torture Lockjaw and Torture Foxy attacking you. But the abandoned demo was free roam. And kinda predicted the runtime demo mechanics, you see in the abandoned demo, you have to turn off the flashlight to avoid lockjaw, in the runtime era, you have to do the same.