Why not let the AH2 community model new planes?
From the top of my head, I can think of these reasons.
1) Development schedule control and commitment issues I've worked on internet projects on quite a few occasions. It always starts out great. There are volunteers everywhere, and everyone is so enthusiastic. However, after the first month of the project launch, people disappear. They break contact, go missing, do not respond and return e-mails. Those who keep in contact did not finish their quota. The project is in trouble, the manager hastily tries to redistribute workloads to people who do remain in contact, blames are thrown around, more people quit or disappear. The quality of work drops down, things have to be done over and over again until it becomes right, and then before you know it, the project is halted.
Then you realize, despite the high enthusiasm, these aren't really committed people you are working with. They are neither your workers nor your colleagues. They are bunch of people with some free-time who thought they'd be able to help things out, and then after a while decide on-line internet committments aren't as important as real life issues. They aren't going to give up their Fridays and weekends to get the work done. They aren't going to stay up at nights to do the quota - they've already done their dayjob, and decide that they need their rest. Some of them are kids, barely out of teens, irresponsible and impetuous, and start regretting they jumped into something they cannot handle.. and decide to just 'disappear'.
Be it unofficial add-ons or mods or perhaps even slight changes to the game, I've seen and experienced how these 'projects work' - they don't.
2) Work standards and regulations The chances are, when people do something they either never meet the criteria, or do an overkill. Things are different when you work alone by yourself. There is no constant input from the management or team leaders who can set your work standards. When people model a single engine nacelle, they might either use 3 gazillion polygons to do so, or use just 3, which in both case HTC would have to either reject it and wait for the volunteer to redo it, or just fix it themselves, which in either case easily doubles the workload. Everything you need to do takes input via e-mail, back and forth, back and forth, back and forth, until you come up with something HTC can use. By this time, HTC could have done maybe twice, or three times the work you've done, themselves.
Relying on people who don't work for you, and thus have no committment to you, is not something a company would want to do.
