I think the only reason people really have for calling it GNU/Linux is to raise awareness about the Free Software movement and its agenda.

The line between "kernel" and "the rest of the OS" is and has always been a fuzzy one. I think RMS would consider GCC to be part of the OS, but I've never seen an Android device with a compiler installed. (And I've sometimes done *GNU/*Linux installations and never gone on to install GCC, though usually I end up installing GCC at some point.)

I don't think it's more "correct" to call it "GNU/Linux" than "Linux" per se. (After all, if we're going down that rabbithole, should I be calling it "Syslinux/Systemd/etc/etc/etc/GNU/Linux?")

But, if you're ideologically aligned with the Free Software movement and want to see more awareness of its mission (and full disclosure, that describes me) then by all means, call it "GNU/Linux" if you like.

All that said, I do think a lot of folks who insist on calling it "GNU/Linux" strongly believe not only that it's good for awareness about Free Software, but also that it's more "correct" to call it "GNU/Linux."

And I'll also say I can kindof understand why people might feel it's more correct. From RMS' perspective, he and some other folks were off building an OS and they had it mostly done and people started using the GNU work with a Linux kernel. But still, that historical argument holds less water every year.