I don't quite understand. Most VPs are pretty close to invisible.

Mike Pence was invisible until the 2020 election when he was put into the spotlight via the false hope of Trumpers that he had the power to overturn the election.

Joe Biden was invisible for the entire Obama presidency.

Dick Cheney was not invisible during the G. W. Bush presidency, and everyone was terrified he was going to force-choke them. This was not a good scene.

Al Gore was somewhat visible through the Clinton presidency, especially towards the end when he was the presumptive successor. (But the climate change attention was mostly unrelated to his vice presidency.)

Dan Quayle was invisible through G. H.-W. Bush's presidency, except when the media needed some (mostly well-deserved) laughs at his expense.

G. H.-W. Bush was not invisible through Reagan's presidency, mostly because he had an extensive understanding of international affairs, unlike Reagan which had, um, let's say "not very much" to be generous.

Does anyone even remember who Carter's V.P. was? Oh, wait, Mondale! Yes, sure, Mondale was a very active V.P..

Rockefeller was a strange case because Ford was himself trying to show he could fill the shoes of the presidency by appointing someone prominent. Ford spent most of the presidency sidelining Rockefeller to the extent that he could.

Until Nixon was impeached, Ford wasn't at all prominent. It was Nixon's show.

And so on.

So isn't the real question: why would we expect Harris not to be invisible? She didn't need to be prominent to shore up egregious weaknesses in the President's areas of competency, and that leaves only 3/7 of recent vice-presidencies as being somewhat prominent. (2/6 if you accept that G.W. was pretty much out of his depth in every aspect of the job--not hopelessly so, but noticeably so.)