In the Computer Shopper case, it was mostly about price discovery for things you wanted to buy. You wanted X. You flipped through pages to find a good price on X.
It was also how I found out that I could now have a whopping 2GB hard disk in my own machine - or that I could upgrade my 486 to a pentium with this cool new thing called the Pentium Overdrive. Computer mags were especially exciting because you got to see the progress of technology.
I think most people back in the day came away from these magazines wanting more things they didn't even know existed prior to opening it up.
People like reading ads about products they're interested in. I know I do. This idea that ads are all toxic because their purpose is to sell just isn't right.