I think that's part of it, and another part is that GNU failed to pick up the Linux kernel early on. I think if they had quickly recognized, "hey this is a great way to complete a releasable version of GNU OS, at least for an initial release" and put out a preliminary package of some sort, labeled as the GNU operating system with Linux kernel, people would've called it that. The fact that the distro packaging went the other way—people from the Linux community, not the GNU project, plugged together parts of the unfinished GNU OS and the Linux kernel—meant that it got more associated with the name Linux.