@robrechtve
If PvE only servers would kill the game because 'every PvE-er would flock to them', then The Arena would have killed the game because every PvP-er would have flocked to it.
PVPers and PVErs are completely different player bases, you can't compare them together. The reason why adventure mode didn't die for the PVPers when they added arena, was because there was incentive to still play adventure mode as a PVPer,
Arena was made for people who ONLY want to PVP, no tuccing, no stealing 50,000+ gold, it was made for ship v ship and PVP combat. If you are a PVPer, you can play both adventure and arena, because you have incentive to play both.
You have incentive to play adventure because you are able to tucc on someone's ship, explode them with kegs, and steal their hard earned loot they spent hours trying to get. You have a REASON to play adventure.
With a PVE only mode, the only people who would play that are PVErs who don't want any fighting. Which means that specifically for PVErs there is no incentive to play a game mode where you can lose all your loot. You would much rather play a mode where it is peaceful, and you can do your voyages in peace, rather than play a mode where you are in constant fear that you could die.
It also goes against the core of the game to have a mode for players who don't want to sail across the open world, but just want a quick, action-packed session of looting and shooting where they're guaranteed to have lots of combat with other Crews without any Forts, Skelly Ships, Karen, Meg, TTs or Journeys getting in the way of pure PvP combat...
But that exists. And it didn't 'destroy the game'.
Again, what I said above, there is no incentive for PVErs to play a mode where they are terrified of being killed, when they could just play a mode where they are safe and sound. The reason why this is bad is because PVPers rely on PVErs to provide the loot.
If PVErs are removed from the game, PVPers will leave, and the hundreds of streamers who only steal loot will leave the game, SOT will lose popularity from people like Pace and Summit, so they will lose a MASSIVE amount of their player base. SOT will not die by keeping adventure mode to 1 mode, so there is no reason to change it.
If you genuinely believe that adding a PvE Only option would ruin the game, let me assure you:
Ultima Online got a PvE Only option and it didn't die because of it, it got more popular and better, including the PvPvE part. (It died years later because of age and an ill-advised attempt to 'update' the game by adding really ugly 3D).
World of Warcraft got PvE servers when the beta proved that 'always on faction PvP', originally a selling point of the game, really sucked for low level/skill players and it didn't get worse (well, not because of that, any way) and still isn't dead. (Why? Why won't you die, WoW? Go into the light!)
Out of all of the WoW clones, only the ones that had PvE Only options survived, because while a lot of players in the WoW community during beta claimed that 'always on' PvP was awesome, the games that actually listened to that soon discovered that past a certain point retention of new players dies off once there's enough greedy players with experience and skill who like to give new players a 'lesson' (spoilers: not an actual lesson) that even if each one of them individually only attacked one player per day, there were enough of them that new players were getting constantly destroyed.
Again, those games don't have massive communities built around stealing other player's loot. Like I said above, Pvpers rely on PVErs to get them their loot, so if you take out the PVErs and give them a private server, PVPers will completely leave the game and the game will be changed forever.
At the end of the day, it's up to the developers to decide what they want to do. The developers have said many times that they want people to be together, the PVPers, PVErs, and RPers. That's their vision for the game, and that vision won't be compromised because there aren't enough people leaving SOT since there's no PVE only mode.
The only way a PVE mode would be added is if they had an absolutely massive amount of players leave their game for that reason, if that doesn't happen, it will never get added.