Why would a "delayed loudspeaker" be so expensive in the 1970s?

Recently, I read about some major musical concert held somewhere in the USA to a record-large audience.

Since there were so many people, not all could see or even hear the music from the main loudspeakers.

Therefore, they put additional loudspeakers far away from the scene, connected with cables from the main equipment at the stage (presumably).

Since sound travels slower in the air than electrical signals inside cables, the music coming out from the far-away loudspeakers would have been out of sync with the actual sound waves, unless they did this "clever trick".

The clever trick apparently consisted of them spending a huge amount of money ("the cost of a new car per loudspeaker") on then-cutting edge electronics which delayed the signal exactly so that it would match the sound waves, and thus not cause disharmony.

While this made me think of how clever that sounds, I don’t understand why exactly this would be so costly, even if it was in the early 1970s. In fact, I don’t understand why it had to be so technical at all. It seems like this could’ve been accomplished in some analogue manner, very cheaply. The cost of a new car, many times over? Really?

What made it cost so much money? And had nobody ever held a big enough concert before this relatively late date, which would warrant a similar solution?

Did they have concerts for many years which sounded bad for the people far away, because the real audio waves were mixed (unsynced) with the local loudspeakers?

And if they barely heard the music so far anyway, did it really matter at all? Or was this more of a way to sell tickets by claiming a "perfect hi-fi-quality experience for every single participant"?

(Sorry I can’t remember the name of the concert; I thought I had it bookmarked.)