This is a piece written by Jeff Jarvis who was a founder of Entertainment Weekly and then a long time professor focused on innovation and journalism.

https://en.wikipedia.org/wiki/Jeff_Jarvis

So, it's a term of art, and i'll even agree that it's got a bit of a tech-y pejorative lean to it, but it's in wide use, and Jarvis certainly isn't solely a person who comes from tech.

Certainly in the UK the 'legacy' part of media orgs (print) is still far more profitable than the pennies paid for ad-clicks.

No history to be found here, but the phrase 'legacy media' started making sense to me, in Australia, when it became obvious to me that said legacy media were being intentionally dishonest / obviously biased in their reporting of progressive topics like renewable energy and fiber optic internet roll out.

'Legacy' basically meaning a representation of the past, not the future.

I'm just realising that Google is pretty much 'legacy search' given that the choice is generally between paid promotions and scams (which could be two ways of saying the same thing). AI may actually have saved Google as their search results were enshittifying themselves into oblivion.