The bronze age changes that didn't stick

[DC Classics]

He moved into the penthouse because Dick graduated high school and left for college. And Bruce decided it was time for a change and get back to the "old days". IRL, of course, it was part of an effort to change the tone/status quo of Batman and probably to further distance it from tv show (which was already happening - the cover date for the issue he moved in was Dec. 1939). There was some very un-campy stuff then. And more "realistic" stories and just part of the general silver-to-bronze shift. Definitely in the letters pages you'll see people who think the comic is sort of going back to golden age roots (not really true, IMO, but opinions vary).
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Bruce actually donated the Manor when he left. It was the past and they moving towards the future. But then they revisited the old Batcave a couple times and, after a decade, moved back in. I don't have that issue. May try to hunt up panels, though. It was a 1980s issue, so Dick had dropped out of college...maybe they didn't have enough bedrooms in the penthouse? :P

They finally moved back into the Wayne Mansion in Batman #248 (1982) "Shadow Play" written by "Gallopin" Gerry Conway, with art by "Gentleman" Gene Colan and inks by "Santa" Klaus Janson, under the editorial of "Dandy" Dick Giordano.