Maybe Toyguru wanted the Star Sisters as much as he wanted He-Ro so they were bumped up in the production schedule.
He-Ro was very obscure yet tooling dollars were used for him before other mainstream characters just like the Star Sisters. The good thing is that they have been released when this line is at full strength. I think He-Ro was a big gamble because he could have flopped and ended the line as fast as it began.
As for who's buying them? I'd say everyone who's forced to buy them with their subscription service.