I think many players are put off by the fact that this is : 1) a "hardcore" sim (no easy targeting mode; with 2) a MP focus, although it is very playable in SP; with 3) a limited, tactical focus since you can only play the few hours around a convoy attack in real time.
I think it is really a question of what players are looking for in a subsim.
Personally I think Wolfpack is currently the best subsim on the market and what hardcore players have been wishing for for decades. It has the most realistic simulation of U-Boat systems ever seen in a simulation (just controlling the dive systems is a game in itself), convoys zig zag, enemy escorts are deadly, nights are black, night surface attacks are very satisfying (and scary).
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