Let’s tell a hypothetical murder mystery to show why some plot subversions work and some don't. The mysterious and somewhat sickly Zachary throws a dinner party at his mansion and invites Alice, Bob, Clara, Daniel, Eliza, Frederick, and Gabrielle, all of whom are his mortal enemies who he’s been blackmailing. Later that night Zachary turns up dead of a gunshot wound. Alice, Bob, Clara, Daniel, Eliza, Frederick, and Gabrielle all have a motive and an opportunity but they all vehemently deny killing Zachary. The obvious solution is that one of the seven house guests killed him, and is currently lying to save their skin. Let’s try out two subversions. Number one: none of the house guests killed Zachary. Zachary, who was already dying of a terminal illness, decided to commit suicide with the hopes of pinning his death on one or more of his most hated enemies, dragging them down with him. Number two: None of the house guests killed Zachary because Hal the burglar decided to sneak in during the party to steal some of Zachary’s stuff. Zachary tried to confront Hal and he shot him in the face.
Why does the first subversion work so much better than the second one? Well, I already mentioned that Zachary was sickly. I didn’t say terminally ill, but that’s not a gigantic or implausible leap from “sickly”. Secondly, it was made clear that the house guests were his mortal enemies, so it made sense that he would do something to tear them down, even at the cost of his own life. This ending may not be the single most expected outcome but it still makes sense, thus it’s a perfectly serviceable subversion. Again, having one of the seven party guests be the killer isn’t the world’s worst ending, especially in this very vague nebulous version of events where all seven basically have an equal chance of being the killer, but in this ending the seven house guests are essentially red herrings, and by Zachary’s design and not the writer’s - he wants you to hate the house guests because he hates them. It’s almost better than just having one of the house guests kill him.
Now, let’s explain why the Hal solution doesn’t work nearly as well. Sure, it’s not the most impossible thing out there, people die in home burglaries fairly often. It’s not like Zachary was murdered by aliens in this otherwise realistic setting. But it’s still not a very satisfying answer. One problem is “gee, it sure was convenient that Hal broke in during the dinner party full of other people with motives to murder Zachary. That’ll sure save his skin!” Hal could have broken in at any time but he did so at just the right time so that the audience could waste their time considering seven other suspects. It feels contrived, as opposed to the first subversion which had a valid reason as to why Zachary turned up dead during the party. Second, Hal wasn’t mentioned during the intro to the story. He’s not a Chekov’s gun being fired in the third act, he’s a random agent of chaos. Third, Hal has no motive and Zachary has no reason to hate Hal besides him breaking into his house. Having random burglar Hal be the killer throws out everything set up in the first act, Alice, Bob, Clara, Daniel, Eliza, Frederick, and Gabrielle were a waste of time, Zachary’s illness ends up meaning nothing, and Hal choosing to break in during a dinner party feels like a contrived coincidence. The only thing the Hal solution has over Zachary killing himself or having any one of the house guests kill him is the sheer fact that no one would guess Hal because no one knows he exists until the end of the story. Most people would guess one of the seven house guests, but maybe somewhere, someone would guess the correct answer that Zachary killed himself to frame the guests. Your options are A) the obvious, unsurprising, but perfectly valid option (one of the guests), B) the surprising but still plausible solution that relies upon previously set up elements but someone maybe somewhere might have guessed it (Zachary killing himself), or C) the totally left field option that no one would ever guess in a million years but throws out basically the entire story for the sake of subversion (Hal)? Well, how far are you willing to chase surprise?