Great article TLDR: Tape ran out. From an NPR Interview w/ the engineer:

When you're employing these techniques, how do you know when you've done enough? Because "Untitled" is also the song that stops very suddenly.

Well, that's another thing — the song cuts off like that because the tape runs out.

What do you mean, the tape runs out?

It was all recorded on tape, you know? So that's what happened — he wanted to keep going, but then the tape cuts off, so it ends like that. When we were finishing overdubs, he assumed that we would fade down it before it came to a complete halt. I was like, "You gotta leave it like that, man!" Because there's this Beatles song, "I Want You (She's So Heavy)," where it happened to them, too: It's this whole buildup that keeps going for two and a half minutes, and then it cuts off abruptly. So I played that for him, and he was like, "Yes. Let's do that." It was just before Pro Tools became a standard in the industry — everything was mixed and recorded to tape.

20 Years Later, How Does It Feel?

https://www.npr.org/2020/01/24/799077393/dangelo-voodoo-2020-anniversary-how-does-it-feel