You need to think that Geordie Shore actually was quite close to BB16 in the ratings, so a fair bit of more people know who Scotty is (I don't like him though).
To you, they may be non-entities, but for BB's demographic, they are certainly not that. You need to remember that there are a LOT of younger people watching the show, people who won't know someone from Eastenders, Angie Bowie, David Gest etc... I notice a lot of people only know Scotty and Megan.
"Celebrity" is a fluid word. Some people will call some people celebs but others may say "how are they celebs?". They are to a lot of people. Just because you don't know them, doesn't mean they are not known. It's all about your age.
The series has a real mix which will make younger and older viewers happy despite not having huge status stars.
Hollyoaks is seen by a younger audience, so it's more likely that Stephanie is known by under 18s, and EE has an older audience so its more likely that over 40s will know John.
David is known by people over 40 for his marriage to Liza, David is known by people under 30 for his participation in IAC.
Angie is known by people most likely over 50, for me, I had to google her to realise who she was. On line, I see that a huge majority of Under 20s didn't know who she was, but a big majority of over 50s did.