I think this is an interesting point! I feel IL-2 is very tailored towards single player, and the multiplayer scene hasn't recieved much developer focus.
If most of the development time goes into single player then why would people want to play multiplayer?
If time was taken to focus on some multiplayer additions I think those stats would quickly change.
I personally really love multiplayer but it can often be extremely boring/ frustrating as in-game coordination is non-existent.
While it is possible to join team speaks or discord servers, it is not nearly as enjoyable nor realistic as in-game solutions and can often be annoying to find the correct servers, channels etc.
Obviously we have the air marshal role in development, but I really struggle to see how it will help to encourage any multiplayer coordination as it will still not have any communication besides easy to miss text boxes. and I don't really see a message saying "Hey, Frogface. Go shoot the tanks" as being very engaging or different that the current multiplayer model.
I strongly feel that a basic yet realistic in-game comms system would greatly help the multiplayer scene as it would encourage more teamwork which is currently sorely lacking. I think this could work really well with the air marshal role too. The air marshal could organise a small team at an airfield, the team could then use the radio to coordinate between themselves. Once back at base they could then update the air marshal on how the mission went which they would in turn relay to the rest of the pilots in the server furthering the battle.
The real issue is that even a simple system would require some dev time to create and implement, which means that's less time spent making planes and thus money. The team can't exactly sell us a comms system, and if they did it would be a big mistake to lock fundamental features behind a pay wall. Instead I think multiplayer could be better utilised as addition revenue sources, if co-op was better realised I would love to buy co-op mission packs to play for example. I feel not everyone would agree but I would also love to purchase (realistic) skins for my aircraft or nose art. these things could help to justify the costs of developers building on the multiplayer framework.