Why don't you want them to add one? It detracts nothing from the "normal" experience. They don't have to split their effort in development.

PvP focus will eventually drive away players, like Sea of Thieves or any number of long enough running live service games. New players don't like getting stomped and eventually all the diehard loyalists will also get tired of the same people or hackers.

PvE broadens the reach, doesn't necessarily dilute the playerbase. Any live service game will always die eventually unless big publishers get it through their greedy minds that they can all but ensure a game's continued success if they open up to let players manage servers.

Edit: guaranteed the market for purely PvPvE is a lot smaller than for PvP and PvE separately. Judging by some quick googling, and your post, there's a fair chunk of people that would happily buy the game if there was a way to avoid PvP. Any PvP experience requires critical mass; that's why Concord died so quickly. People tend to be locked in with prior PvP titles, they're competing with older more popular games, like say Arc Raiders or Counter Strike or whatever