We all know that the Precursors were attempting to find a cure for the virus when disaster struck, in the form of a pretty p****d Sea Dragon, who released it into the general population. Realising that they had majorly screwed up, the Precursors then did the decent thing, they set up a massive gun that would happily shoot down any passing ship regardless of whether it actually wanted to land and then turned themselves into data chips so they wouldn't have to face the heat. They left a few data clues for those unfortunates stranded on the planet and then by a complete coincidence managed to scramble the location of the caches which apparently they had hidden their data chips selves away in.
So far so good. Before they became Bits and Bytes for the rest of eternity, during a meeting which I suspect followed a heavy night of drowning their sorrows about the total cock up they had engineered, someone said "What if someone actually survived the Big Gun, Shot Down scenario, got off planet and told someone?" So they added some bio engineered Cyborg assholes to hunt you down and tear you apart with their funky purple mantis hands. Yay Precursors! Clearly they had forgotten that the Planet already had some pretty efficient natural predators that were ready and waiting to stalk you, scare you into a heart attack and chew off your face.
There is a good reason however that they weren't entirely thinking straight and I think I've found it. During one of those moments where you're trying to set up the perfect screen shot moment because you have organised your base and can't think of another valid reason not to go looking for the Lava Castle, I happened to notice something which in HOURS of playing had never shown up before. I've farmed plants, built platforms, hacked table coral and generally swum aimlessly all around my base area for the entire time I've been playing but I only saw it after I got the Cuddlefish from the Precursor Cache in the Lost River.
Firstly I have to assume some stuff, which, personally I think holds water (Pun so intended)
1 The Cuddlefish has all those Tentacles to enable it to use tools, these being primarily a simple Table Coral Chisel and a large rock,
2 It's affection for humans makes it want to let us know the real truth that the Precursor's tried to hide,
3 They knew that, so they exterminated all the Cuddlefish except for five eggs which they thought were hidden well enough from us to never be found,
4 The Precursors sucked.
Taking those points as truth I can understand this strange event.
During my swim about to get the shot I was after I noticed that someone, or thing had apparently carved me a statue into the very rock my base is built on! It wasn't there before, I would definitely have seen it. But it points to an Ancestor of the Precursor's that explains all the douchebag things they have been doing and why they were unable to create the Vaccine. It explains their apparent obsession with Eggs and where they really went. I don't think they are really in those Caches as some kind of sophisticated flash drives. I think they simply flew away! So (DRUM ROLL PLEASE) I present to you my theory on the REAL story behind Subnautica.
Many years ago after a failed Hollywood career and a single film that bombed an ex actor went off into a sulk and found a new planet. He could do so because he had the natural ability to fly! Having failed at acting he took up microbiology to earn a crust and fiddled about with the DNA of a few creatures that lived indigenously on his new home. Following a power out in his Lab some of the DNA was infected with a Bacteria from a mouldy sandwich he had forgotten about in the back of the fridge in which he kept his samples. Unwittingly he then used the DNA and managed to create the virus which then infected the whole planet. When he realised what he'd done his cry of dismay became the name by which the Virus was known. By this time he cloned himself as well as he'd become a bit bored, after all how many games of Solitare can you actually enjoy, and he and his copies had a bit of a melt down when they realised what had happened. So after trying a bit to fix the problem and realising he couldn't he stuffed his clones into USB's, built a massive gun to stop anyone finding out, flew off and pretended he'd been living in Hollywood obscurity all the time.
EVIDENCE (Some of this is even true!)
The Precursor's settled on the Planet from somewhere else and had to have flown to get here. The Precursors MUST have been as at home on water as on land or they would have been Reaper food extremely fast and never settled the Planet.
The Virus turns you green (this is very important as I believe his cousin, visiting in an attempt to convince him to turn to TV instead had bitten the sandwich at some point and it was some of the Bacteria from his saliva which started the whole cycle.)
The Name of the Virus, when spoken out loud sounds suspiciously like the call of a water fowl, and incidentally mirrors the name of a GOOSE! in Watership Down, another Movie.
The Precursor's had unknown space technology which we haven't encountered before indicating they came from a far distant undiscovered planet to Alterra.
My Cuddlefish carved a statue of the offending party proving that every crime will eventually be outed ;)
And so finally I present my photographic evidence which I think you'll agree us a pretty damning final note. (There's even a link to Marvel which makes this almost 100% certain to be real)
(If you don't know who that is then this whole thing was lost on you completely :)