Don’t you mean a scubado?

The problem is they had a seven-ish hour pre cut, a four and a half hour directors cut, and the two and a half hour theatrical release. The original pass on the movie probably explains everything. If I’m being honest I’d gladly give up the karaoke scene for the 10 or so 30 second explanation scenes we could have had in it’s place.

In the case of Project Hail Mary they have an “answer” as to why. The book directly explains it and the movie nods at it in a scene where he writes “Muscles?” on the white board, but its the coma robot, Armindo. It was meant to work their limbs and apply electrical stimulation so they wouldn’t atrophy on the trip.