Your question is about the same problem, but in to different environments. I'll then separate them as they'll ask for different approach. In both cases, as it stands, a single "why" is very aggressive. No wonder why people jump out of their way, as "why" questions often lead to an unproductive or hostile response. People don't like to feel like they have to justify themselves.
- The workplace setting
I've but only failed when I was doing like you do. I quickly understood I had to be more polite, and provide people with "sugar-coated" helpful questions if I wanted them to not feel like they were being "verbally assaulted", but also be more inclined to respond positively. You'll find hundreds of links about the best way to nicely ask people according to the situation. Some very simple examples.
In your case: you know the software / application but not the reasons of the colleague for asking. Step in their shoes: why do they need this? If you want to be helpful, show that you're willing to do your best. You can simply ask for clarification while you tell them why you ask. ie: is this for doing X/Y/Z? I'm asking because I can do A/B/C or give you this as an extra tool if needed. When doing this, I often had an answer to my "raw why in disguise", plus the considerations of the person. It's much more efficient and strategic, without being aggressive at all. It's a small inquiry in order to offer for extra help.
- The friends setting
In this case, the "why" is also very aggressive, and almost an accusatory tone, close to a patronizing effect. Instead, expand your "why" by showing genuine interest. Your "why" must lead to a wider explanation. ie: you like A/B/C?! Sounds interesting! I'd really like to know what you find interesting doing this. You tell me more about it maybe? You get the idea behind. People will be able to share only what they want to. Because you ask an open-ended question. You don't push them. They don't feel attacked. Therefore, more willing to answer.
To summarize, I'd say that you need to put more nice words into your sentences when you ask people for feedback, reasons, or any other topic. You ask questions, well, by asking questions :) Real and complete questions, with words, that "why?" alone isn't...