I don't know much about AKB or it's sister groups, but from what I've seen Sakura was one of the more popular members. She easily could've stayed in Japan where she already has an established fanbase and rake in the cash, but instead she decided to try debuting in a new group after 10 years as an idol, doing difficult choreos, speaking a language that's new to her, and face the scrutiny of the public when the sentiment towards Japanese isn't good.
I think being on produce 48 lit a fire in her because ever since then she's been steadily improving for someone who's been famous for so long
Should could have stayed in Japan and continued her fanbase there but she's choosing to pursue her dreams 
