As someone who followed them since debut, I always questioned that. Solbin was everywhere, the agency tried all they could to push her as an "it girl". The songs which they had were public friendly. A lot of people say "X group should hit big in Korea" but they don't even notice that many groups don't release their music to appeal to Korean fans. In LABOUM's case, they were exactly releasing what Koreans would enjoy.
The girls had a few controversies in 2017, and then slowed down with promos, but they were a 3 year old group at that point. The key to a group succeeding back then was the early years (Yea it wasn't like now that even a 10 year old group would stand a chance lol)
Journey to Atlantis was played on "How do you play " which is a very popular show but not like they weren't on big shows before.