Prerecording the musical soundtrack has been standard practice since very near the beginning of the sound era. Busby Berkeley apparently introduced the practice. In addition to the reasons mentioned above, it makes choreography and rehearsal much more manageable.

Even tho Zac Efron is a singer, he did not sing in the initial "High School Musical" film because the musical soundtrack was recorded before he'd even been cast in the part.

It become standard practice in television for performers to lipsynch because it saved producers setup and rehearsal time and it made it easy to time the segment.