I wonder how many people actually used those portals, as in clicked the links and browsed the directories. I don't think I ever did, but I was just a teenager and not American, so maybe I wasn't in the target audience?
In the early days the portals were great and you could find most anything by browsing them; click on topic, go through the subtopics and get a list of websites on that topic, if those did not have the information you needed you went to the links pages/web rings on those sites and you would get what you needed soon enough. It was quicker than scrolling through pages and pages of modern day google results and trying to game the search terms. These were all personal pages you would be browsing and one of the things you would do in those days to get your page noticed is register it on Yahoo and the like. You were able to explore the internet in a way you can't anymore.
I did at times, but they are more fun now, browsed through the Wayback Machine.
Not only for the nostalgia, but for some topics, like som games or game genres, it can lead into amazing old internet clusters of sites full of fun/useful content (i.e. not just the ad/clickbate stuff everything turned into later, but real people just sharing because they wanted to share).
Many ISPs set a portal as your browsers homepage with their installers. Most people didn't know how to manually set up dial-up networking and would just run an installer their ISP provided. Since they didn't know how/why a portal was set they just assumed it was how things were.
