Look back at the time, FF was supposed to be a massive era. The era has so much potential but Britney ****ed it up big time. It could have been as big as Circus or even bigger if Britney was into it. Reasons I say this are:
1. The hype: It was huge, very huge. HIAM debuted at No.1 in several countries and broke digital and radio records in the states. They should and could have saved HIAM from free falling but they didnt do anything. Britney was fishing at week. Her team didnt release the video until 6 weeks later. Those 15 video teasers kinda killed the excitement. Britney didnt perform the song until it already died.
2. Massive radio support: Britney had never been a radio favorite before FF era. They definitely were on her side but she wasnt into the era so sales couldnt be bigger.
3. WW tour: its tickets were more expensive than Circus tour's tickets and she reached more continents too. There are some huge dates in South America but the demad was so low due to Britney looked dead and lazy. If FF tour was sold out everywhere, it would have grossed more than Circus tour too and who knows? She mught as well add more dates.
4. Media: They kissed her ass after those BBMAs performances with Nicki and Rihanna.