Why did FF Tour get pre-recorded vocals?

[MoodRing]

First off, there is no shade here regarding the VMA performance, I loved it and have no REAL issue with the playback.

 

However, knowing now that so little effort from Britney or her team has been put into pre-recording for Vegas/VMAs, I'm genuinely curious as to why FF got lots of pre-records? To me I'd think it was obvious that if someone thought it was necessary for FF, that the same parties would think it VITAL for something as important as Vegas?

Britney fans, I'm puzzled, what's your thoughts?

[Pikapi]

#JusticeForUp&Down

[BTI485]

Because her dancing was bad like really bad then

[TomLondon1992]

Because it was an international concert tour and she would get criticised by international media for lip-syncing. Vegas is more of a show, all about the visual and the performance. 

[Pp35]

I always thought it was because she got so much hate on the circus tour for lip syncing but idk 

[K-J]

I don't think we will ever know why she lip synchs, pre records vocals or doesn't.  One of the many mysteries.