Yes this makes sense. I’ve been using terminals for years with the ‘copy on highlight’ feature enabled, and I’m pretty sure when I was on OSX it was a single buffer.
I can see how having mouse selected text end up in the buffer on a non-Terminal app would probably not be the desired behavior.
I found ‘autocutsel’ which will keep PRIMARY and CLIPBOARD in sync, however Gnome Terminal doesn’t seem to support ‘copy on highlight’ while Terminator does.