Leagues that are less than 3/4 full are a hard sell as people want to beat people. IF you want to fill a league and keep players interested in it, it takes time and effort. In the Leagues I run I like people to know about the players not only on their team, but the players on other teams as well.
I like people to identify with the team they own, have a say in team name, location, stadium, team colours etc in my 2nd league I renamed around 500 players after the initial draft with links to the teams, the Arkansas Buzzwagons with their Wacky Races theme are a fun team to play against. The Guinea Pigs have players like Kevin Bacon, Porkchop Hill, Piggly Wiggly, Boss Hogg, 'Babe' Ruth.
The Kandy Canes are all about Christmas, where else can you play against Rudolph Rednose, Kris Kringle, Buddy Elf, Black Peete, Saint Nicholas, Donner Blitzen and more.
A league is what you make it, if you want to fill it and keep it full there needs to be a reason why people want to be part of it. Yes, I'm recruiting for a 3rd league and I'll wait until I have 32 owners on board before I create it. That gives it the best chance of survival.
Sometimes the best thing to do for something that's dying is to let it go. Maybe half of the remaining owners will move to other leagues, maybe they'll walk off into the sunset.