They definitely felt a little tacked on back in Races of Stone.
Actually that was we're they were most interesting, because it was the one time they got meaningful lore, other side of that while individual characters have popped up in novels and even the Book of Vile Darkness movie, and such, they really haven't gotten explored as a culture or species, for a race as popular as they are, they don't feel properly explored leaving them feeling shallow.
If they wanted them to be a PHB race, more effort on the lore should have been done. Elves & Half Elves, Halflings, Dwarves, Humans, Orcs & Half Orcs, Gnomes, Tieflings, Gobliniods, Genasi Aasimar/4eDevas, all have rich, deep histories with piles lore, and a meaningful place in settings.
Goliath's were an after thought for FR & Eberron lore, they are in a few mountain ranges and those Goliaths are stone Goliaths, that is just about it, with a few minor exceptions.
Other 5 subtypes don't even have that, no idea how they fit in with FR lore or Eberron.