No other explanation? Try the explanation that Floyd swallowed a bunch of the pills he had to avoid being caught with them and died of a consequent overdose. Which, based on the evidence, is what apparently happened.
I think the prosecution has pretty much been forced to abandon their early "choked to death" theory and are moving to a "Chauvin should have rendered aid" theory. That latter theory has severe problems as well - Floyd's actions and the threatening crowd made releasing Floyd from restraint unsafe for all present. The Defense is shredding the Prosecution's case in the cross-examinations of Prosecution witnesses, cross-examinations being limited (as I understand it) to matters testified during the Prosecution's questioning. Unless it began today, the Defense has not yet begun to present its case.