Marketing. Great over-generalisation but a lot of Fairport's continued following rests on rousing the troops at the annual Cropredy beer picnic. Having not had a great or charismatic singer since the early 1970s, they've successfully gone for the beery blokes. It's basically pub rock meets rugby club with jigs'n'reels, and they've built a significant community out of that audience. Steeleye never had that marketing drive. Neither band have musically produced much of real significance since their innovative years when they were hungry and motivated, but as barnetfolkbabe said, Fairport have definitely been much better at keeping in the public eye. And as somebody else said, since SS were considered 'folk' and FC 'rock', the latter have been helped more by the rock nostagia press too.