Why did the Devil's triangle curse only Captain Salazar and his crew? Surely there were previous ships that entered the triangle before this. What happened to them?
Even Henry's ship enters the triangle but is unaffected by it. Why?
According to Wikia:
According to legends, many of the ships that entered these waters vanished without warning or explanation, leaving only a few lucky sailors to recount the monsters, storms, ghosts, and pirates responsible for their misfortunes.
But it's also mentioned that:
However, the supernatural forces in the Triangle revived Salazar and his crew as powerful ghosts, granting them vast powers and abilities, though keeping them imprisoned within the Triangle for decades to come.
So we are to buy that some supernatural explanation.
The Devils Traingle is a geological location with supernatural properties that was,
... A place where the dead live and the living die, the Triangle was avoided by every sailor worth his salt.
Salazar's ship, the Silent Mary, was almost completely destroyed in a series of explosions, which caused the deaths of Salazar and all his men. However, the supernatural forces in the Triangle revived Salazar and his crew as powerful ghosts, granting them vast powers and abilities, though keeping them imprisoned within the Triangle for decades to come.
Everyone who enters the triangle basically becomes "cursed" similar to what we have seen throughout Pirates of the Caribbean films, most notitably with Brabossa's crew in Curse of the Black Pearl.
Many years later, a down on his luck Jack Sparrow traded his compass away for a bottle of rum he incurred a terrible price. For dishonorably trading the compass away the thing he feared most, Armando Salazar and his crew were set free; the entire Triangle shattering and sinking to allow them their freedom.
However, the reason Salazar has escaped, is because of an additional curse that relates to Salazar through Jack's compass by "betraying it", causing 'the thing he [currently] fears most' to come true.
So it seems likley that others WERE trapped as cursed 'living-dead' ghosts in the Triangle, and probably most were not be able to leave, but considering the Triangle sank, it seems likely the others [who could not escape] sank with it and it's unlcear then if they remianed living-dead trapped under the ocean or if the magic/curse was broken (by the destruction of the Trident) and they "passed onto" the other side?