They don't "own it", but the point is that it would be a pretty big source breaking change that should really be avoided unless completely necessary. Even if those libraries didn't exist, it would still be a source breaking change.
I will point out that these aren't the only examples of libraries that break due to the /.../ syntax. As @mishal_shah pointed out, this syntax breaks 16 projects out of the 2968 in the Swift Package Index. That certainly isn't insignificant. I believe that following the precedent set by other languages is no reason to introduce source breaking changes, especially since two popular packages would get broken along with all their clients.