It's a little weird, especially since the musicians aren't visible to the audience - why would you play live?
You may say the audience won't know the difference. But word will get out. Audiences may not be willing to pay premium prices for prerecorded content.
Does the potential for failure and variation attract the audience? Or just the fact that the medium is much higher fidelity: stage actors are human, three dimensional, and no other medium can record all the subtleties of motion and expression just as well.
An concert, a play, or any other live performance is much more than a single night, 2 hour performance. It's countless hours of practice, errors, emotional up & downs during the journey.
The performance one watches is the tip of the iceberg and the underlying depth is what amazes us as humans. The unmistakable performance or real-time and invisible improvisation during the show.
I used to played in a symphony orchestra. Even the slowest of classical pieces is a storm for the orchestra, if not for the spectators.
On a side note, these broadway performers and musicians were awesome and incredibly professional and talented. I didn't know what to expect (as a kid, I found these musicals so boring) but it was great.
Ease and quality of improvisation? Does the musician here improvise? Slight variation in each performance?
The main song in Phantom of The Opera, in the West End, is/was done to a click track - and the performance is/was noticeably flat because of it, in my opinion.
Otherwise why not just fire up YouTube out Spotify