”Molly Mae” is one of the most working class names you can get. Her parents (divorced) are PCs. She’s from Stevenage and went to the local comp. There is nothing posh about her and she’s never claimed to be.
It sounds like you’re confusing “posh” with being articulate. A lot of girls on LI like to put on this dumb girl persona and Molly didn’t. Using “categorically” is not unusual in the real world - it isn’t a big or complex word - but even if it was, having a good vocabulary does not make someone posh. The fact she didn’t pretend to be stupid is probably part of her appeal - it makes her more aspirational as a role model girls can look up to.
She built a career as an influencer herself by vlogging on YouTube before going on LI. She’s a similar “type” to lots of YouTubers popular with young people - sweet, positive and upbeat, relatable and attractive in a “girl next door” way.
She would have had to teach herself the video editing and marketing skills to build her following.
She obviously realised that going on LI would be a brilliant marketing tool to build her following even more so she went on there and she already knew when she came out of LI, after years of building up her following, how to capitalise on her new following and maintain it, which other LI might not.
Tommy is no “sportsman” and is not taken seriously by professional boxers but is a new kind of YouTube boxer. This career only took off after LI and his following is nowhere near as big as Molly’s. He’s capitalised on his brother’s fame and probably Molly to some extent who has helped to keep him in the spotlight.
She might have benefited from being in a relationship in general which again can be aspirational for young girls and many will have enjoyed following their romance.
As for Anna - I have no idea why you’ve singled her out from the many other more personable LIers of all races who never took of. As a fellow Persian I wanted to like her, but she came across very badly in the show. She was incredibly hostile and aggressive at times. It doesn’t surprise me at all that she didn’t have the mass appeal that Molly had.