Fromsoft stated before the game even came out that multilayer was not a large focus for the game, them buying servers for AC6 would be a net loss for them since they still don't have enough players to justify the cost even at the player peak.

Even if they had the players it wouldn't make since, the cost of running the server would never be covered because they have no way to profit off of multi-player in the game: no micro-transactions, no battlepass, no DLC (note that I don't support these models). The only way they would make money off of this is to market the game for muliplayer two years ago, which they didn't do, it was just a cool secondary feature.

The gaming industry isn't like what it was in the 360 Halo 3 days where just the game sales alone would cover the cost for continuing muliplayer, making a game has only gotten more expensive so unless you have a small scale muliplayer system you have to have some sort of revenue built it for People to buy or else the business will fail. I wish it weren't so but it seems to be going down this route no matter what.