I don't understand why people get offended when someone tries to find a motive behind something “So, what’s the catch - is this just a marketing promotion.”

I don't understand why people get offended when someone tries to find a motive behind something “So, what’s the catch - is this just a marketing promotion.” There’s no catch, no strings attached, no BS -- we just want to do our part to give back to the community that made us successful and this is our way of paying it forward. Clearly Braintree wants us to think they are doing it to do 'their part'. Pointing out that this might not be true shouldn't offend you. The parent is not challenging your intellect. He is just making an observation. I got a few negative comments on something similar I wrote about github http://minhajuddin.com/2012/09/29/github-is-not-really-free-for-your-public-open-source-projects http://minhajuddin.com/2012/09/29/github-is-not-really-free-... . Am I missing something here?