Honestly I think you are missing two important facts in your reasoning here:
1. Dual boot was possible far far before Ubuntu was a thing
2. Free Software is about freedom.
Freedom also means being free to use (and even develop!) closed source code but choosing not to do so.
Preventing others to use closed source is not free software purism. It's open source marketing.
Server run by the main developers of the project It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!