This questions is purely about government agencies, not private companies.
Typically the massive reams of data that must be produced to design and qualify a satellite or rocket aren't openly shared with the public. Aside from the 'we pay for it, we should get access to the data' I see a few solid reasons why this sort of work should be openly shared;
- Promote growth in the sector.
- Promote the agencies competencies.
- Show good engineering practice.
I'm sure there are more reasons, these are just the 3 off the top of my head (I'm clearly wearing a weird hat).
As far as I can tell there's only a few reasons against sharing this type of data;
- Loss of profitability.
The second reason is almost a joke, there's so much cross agency cooperation these days that we can barely tighten a bolt without getting the wrench from another country. This leads me to think that profitability is the main reason... is it?