You're pretty mistaken. He wasn't in any kind of restraints or suit, he was in a regular cell in confinement in regular inmate uniform..

If you look at the cell photos he had his personal items and bed sheets, that isn't give to a person who is on suicide watch. They're given a padded room and a smock made out of a material like really thick toilet paper which can't be shredded and made into a rope.

He was alone in a regular cell, he had access to all of his personal and canteen items and regular bedding. He killed himself with the sheets that every inmate is given.

It's not exciting, but people kill themselves in prison all of the time. It doesn't take a grand conspiracy to understand why a billionaire facing effectively life in prison would feel suicidal.