@Lisias, the problem with that attitude is that it can allow for all sorts of modding derivatives (up to and including simple logo changes to show that the original mod is now 'mine') to spawn without the original modder knowing about it. Everybody that has ever dealt with videogame mods knows that plagiarism is rampant in that community, and that easily finding the original source of a mod is not a given.
Asking for it allows the licensee to check whether what they invision is indeed allowed under the license, and it in turn allows the licensor to keep an overview of what is out there, and makes it easier for all parties to look out for stolen/plagiarised stuff.
The transparency and etiquette of the KSP modding community is a needle in a haystack (when was the last time you downloaded a mod for another with a clear license and source code included in the download?), and we should cherish and nurture it. Communication between all parties has brought us this far and has more often then once defused "permission or not?" discussions.
Asking for permission, even though it is not necessary in view of the licensee, is a small effort that can save a lot of time and energy down the road.