The issue is that for a lot of players (and DMs), the idea that "somewhere back in your bloodline" ends basically at "your mom and dad". I actually blame half-elves a bit for this; for at least 20+ years, half-elves were described as being a true-breeding species, sometimes with their own culture (Eberron) but every half-elf I've ever seen is a first generation elf daddy/human momma (or vice versa) blend. (This thinking goes back to AD&D, when literal % bloodlines determine if you were an elf, half-elf, or human).
Which is why I'm fine with moving the idea of half-anything into something other than species and instead making every species a true-breeding one that long ago has some monstrous element to it (if any). Goliaths are goliaths, not half-giants and if you want a human/elf mix, it will be something other than a separate species.