There are different layers to the sport of running. Are we talking about road running exclusively, competitive road running, cross country, fan base, or media coverage? Because you'll get different answers for each.
Road running is more popular now than ever. More races, more participation. However for the most part the races themselves are not very competitive. And that goes from weekend 5K and 10Ks to marathons. There was late 70s-into the mid or late 80s American heyday in road running at the elite/sub elite level and it was popular in the press. That has leveled off, but amazingly more often than not, the times they ran back then were as fast or faster than most athletes today. Check those 15K, 10 mile, and even 10K times from back then. Also, the road races back in the 70s and early were overwhelmingly male and younger male (under 40) dominated. Now more women and masters runners participate/race.
The sport hit sort of a lull in the 90s, and while there were some really good top Americans (Kennedy, Williams, Jennings et al.) the depth wasn't there. And participation rates waned until the 2nd running boom, starting in the mid-late 1990s. There has a been a resurgence at international performance since Meb/Deena had breakout performances at the 2004 Olympics, and that continues.
Meanwhile, however, cross country at the high school level and its competitiveness at the college level has only only grown in the past 20 years. And that's in spite of all the growth from soccer.
Post collegiately, for elite and emerging elite, that has changed a lot. Back in the day, it seemed that more kept going for a number of years and there were more informal/or formal training groups. Now it's go pro or go home (get a contract or get a job). Letsrun itself promotes that. Either you're 3:33/13:06 (4:02/14:52 for women) by age 23-24 or you're a bum who needs to be making $450K a year and making angry-hateful comments on this forum.
And now, the cool kids do ultras and trails.