Actually its the exact opposite. You are equating it to that. This is normal politics before Trump lowered everyone's standards. 30 years ago he ran for President and was forced to answer for his plagiarism. 14 years ago Howard Dean blew up for yelling Byahhhh. Explaining a past position is hardly anything outrageous. And its just one video talking about it. Big whoop.
He isn't being canceled. He is leading the primary and is leading in black voters. And doing so after a debate where his dentures almost fell out and told parents they should play a record player for their kids.
Plagiarism is plagiarism today or in 1982. It was just as wrong 50 years ago as it is today. You always have to answer for something that has always been wrong. What he said was boring then, but now looking at it with what we know about addiction, it looks terrible. It is ONLY terrible in hindsight looking back with modern eyes. It isn't about how long passes for something, it is how it was/would have been judged at the time it was said.
Our past is filled with stuff that was nothing to us back then but today would be labeled offensive. Heck, imagine all the stuff in textbooks we learned in public schools?
Him getting old and answering questions poorly is a very valid reason for not liking him now.