On Monday, 5 October 2015 15:06:03 UTC+2, wrote:
If you are a manufacturer of soaring instrumentation that does computation and display, why would you voluntarily give away your proprietary information to people that produce competitive alternatives for "free"?

You'd want to give away your proprietary information so that you don't lose potential customers and you grow your customer base.
If people want to integrate a manufacturer's product with a free one then it means that they've already purchased or plan to purchase a product from the manufacturer. The manufacturer would be shooting themselves in their own feet by trying to protect their proprietary protocols/implementations.
Let me give you a real world example.

I intend to fit a modern glide computer and vario to my glider next year. My budget is around $2000 but a vario and glide computer combined is in the $4000 to $6000 bracket. A decent vario is non-negotiable so my only option for the glide computer portion is something like XCSoar, Tophat, iGlide, Oudie/SeeYou, etc. which are free or affordable.
This means I need to find a manufacturer that releases information regarding their instruments so that one of the above products can support it.
ClearNav make some great looking varios but the lack of support with free/affordable glide computers means I need to take my $2000 elsewhere.
ClearNav $0
LXNav $2000

What would the iOS or Android app stores look like if the manufacturers withheld SDK's and documentation regarding the systems and API's preventing 3rd parties from creating custom apps?
If Mercedes Benz made a proprietary tow hook on their vehicles would you be happy being forced to purchase an overpriced Mercedes Benz trailer because generic ones are not compatible?

The power of sharing information and promoting compatibility (even with your competitors) is that you create an eco-system drawing in even more customers than you would have had otherwise. Ten customers spending $2000 vs two customers spending $5000?