why did abc move Happy days to thurdays in last seaseon?

why did abc move Happy days to thurdays in last seaseon?
Happy Days didn't air on Thursday during its last season. It was always on Tuesday. What happened was the show was put on hiatus for a good part of that last season. In the summer of 1984 ABC burned off the original episodes that hadn't been shown yet on Thursday nights. Those shows all took place before the Finale which did air as a one hour episode on Tuesday night that spring.

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