at the same time Matsuda Miko got on S1 almost entirely off her name as a former NMB member. She wasn't even popular as an NMB member, most don't know about her, and I don't think her debut was strong enough to warrant getting into S1 either.Yui hatano said she did av because there were too much competition in gravure idolings + low pay and strict guideline to follow if you're a minor member of a huge group like akb or ske. However, nowadays there are a lot of competition in av and low pay as well. You need a decent popularity and look as a fallen idol in order to become a popular av idol. Not every fallen idol will be as popular as shoko and yua mikami. They get good pays because they get a lot of outside opportunities like yui hatano that goes to Taiwan and other countries like half a dozen times a year. Av pay isn't as good as what mihiro said in her interview with abematv nowadays unless you're the one of the best sellers. Some av idols if not most probably get a lot of gifts from fans and wealthy businessmen like yuria satomi offscreen in private. Drugs and escorts are pretty big and some top av idols probably charge a big figure for their body once in a while.
Of course to have "legs" in the industry like Yua or Shoko you have to be pretty/talented on camera but being a former idol from a major group is still a huge leg up.