The main issue with the Raspberry Pi 3B+ is not that KStars or INDI don't run on it as you pointed out, the main issue is that the Ubuntu folks have not put out a new version of Ubuntu-MATE (or any Ubuntu) for the Raspberry Pi 3B+. Also, they haven't yet released a version of the new Ubuntu 18 for any Raspberry Pi yet. They were saying it would be ready by December 2018, but now it is almost January. Ubuntu is definitely not the only way to run KStars/INDI on a Raspberry Pi, but it is the best way in my opinion. I am hoping that they do it soon, but it won't do any good to complain about that issue in the INDI forums since we don't have anything to do with creating Ubuntu here. We should be encouraging and supportive of their getting it ready.
Also you should note that there are no "founders" as you called them for INDI or KStars. KStars/INDI are free, community driven software developed by the people, for the people. There is no cost to use them. Anyone can contribute to the project and dozens of people have done so over the last couple of decades. Also anyone can use the software free of charge. None of us gets paid to contribute to the projects.
We all would like to see KStars and INDI improve over time and would also like to see it get more adopted as you describe. Numerous people have set up solutions for getting it out to the people. Some have made instructions, some have made scripts (like me), and yes some have also made complete images as you have requested. The latter category includes Stellarmate, Astroberry Server, and ZWO's ASI Air (though they have their own stuff in there). Instructions and Scripts don't really cost anything for the creator to put them up there except for time and effort. But putting together a complete image and then hosting it for users to download, that takes significant resources to produce and maintain. Also, each device is different and would require different images. That is why the images and prepackaged devices typically cost money like Stellarmate.
There are completely free methods of getting your device all set up, such as my script and instructions, but those methods will require the user to put in extra time to set them up. If the user wants for it all to be done for him or her, then I think they should look at one of the prepackaged INDI devices or images that are available. The complete system including the image costs less than some comparable imaging software does. Now that being said, if somebody would like to put together an image and get it up there for everybody to use for free, awesome do it, help everyone out! I know that I don't currently have the time or resources to do this, since I have a full time job as well as all the time that I have been volunteering helping with KStars and INDI, but if somebody else can provide that service for free, awesome, more power to you!!
Thanks,
Rob