I think there are many reasons why ACL got more attention in the original run.
Everyone could personally identify with the show. You didn't have to be a dancer. If you had ever been on a job interview, you knew the feeling of "God I Hope I Get It!" Chicago was a story that you sat back and watched, ACL was something that you experienced personally.
One was the context of the times. The US had just been through Watergate and all the media coverage of that and the trials. Some of the public's attitude was that they were weary of the media and trials and along comes Chicago, a musical about media and trials. Too much art imitating life.
Another was that ACL was such a different show. A musical where there was no star. That's a novel idea. As opposed to Chicago which had two stars. And then Gwen Verdon got sick and they upped the star wattage by bringing in Liza.
And ACL really made use of a new idea at the time: the television commercial. I still remember seeing Pam Blair during the commercial break at the 11:00 news singing "Orchestra and balcony, what they want is what you see" and thinking it had something to do with theater but I had no idea what.
If anyone ever tells you that you put too much Parmesan cheese on your pasta, stop talking to them. You don't need that kind of negativity in your life.