As one of those may players, and someone who hasnt played for a month but just came back to see if there's an update, I had a few reasons why I stopped playing
1- lobbies. Most games you just jump into the action, but this game has a lot of downtime where you have to wait for that last 4th player, or wait for a pilot, or play with/against AI which is not fun to me, I like to play with/beat other ships with real people.
People need to exorcise a little bit more patience, imo. I swear if a game doesn't start within 10 seconds of someone joining a game, they leave. Baffles me to no end.
2- variety of gameplay. i got really tired of having to play engineer 90% of the time. pilot is usually reserved for older players, gunners are usually limited to 1 and then the pilot asks you to switch to engy. Also got tired of playing on pyramidions, and when I did get to play on a cool ship like squid we always lost. this lack of variety has mostly to do with balance of ships/classes/guns
"Reserved for older players" is something that's really in your own head, honestly. I've seen plenty of lower level players pilot and be quite adept at it. Yes, you'll want to be comfortable flying the ships that you do, but the only way to get that experience is to, well, do it. If someone else insists on being captain or piloting but you still want to work on yours, you're certainly under no obligation to give into their requests.
As for gunning, if you're on a ship with two engies already and the captain tells you to go engie as well, just tell them that you're working on your gunning. If they then throw a hissy-fit, just block the person and find another ship (there is some point to not actually needing to be a gunner to be a gunner currently but that's an entirely different topic). And if there's a gunner already, well then, find a ship that doesn't have one already
There's also certainly no lack of variety of ships, they all have their purposes, strengths, weaknesses. It's up to you to find out what works well when, and can especially mixed up if you're able to talk to the other captain about how you want to go about in a game plan.
--> If there were more classes (which I dont think is planned) or even sub-classes (Co-Pilot, Main Engineer, Associate Engineer, Main Gunner, Associate Gunner) and those classes had distinct sub-roles then itd be more fun
Sorry but, wha? What exactly would this accomplish that can't be done be simple in game communication? Heck, what would a co-pilot even do o.O?
3- no social aspect. should really have an integrated clan feature. this game is really meant to be played with friends, then it gets really fun. if you're running solo, ur gonna get tired of it quickly. and thats what happened to most may players
I personall ran solo for... quite a while and never got tired of it. While the game (and any game) is enjoyable when you've got friends along, that doesn't mean you can't make them in game. A high amount of folks in the game are incredibly friendly and supportive, but if you're closed to the prospect of talking to others in game or here on the forums, yeah, you won't really get anywhere.
Also, iirc, clan/team/guild/whatever support should be in game in a near future patch.