The Europa League is considered a B-cup through most of Europe. And after playing in the Champions League 11 times in 13 years playing in the B-cup isn't considered interesting enough. We used to meet Real Madrid, Bayern Munich, Juventus, Arsenal, Borussia Dortmund, Inter Milan and so on every year. Meeting Rapid Vienna, Metalist Kharkiv or Bayer Leverkusen doesn't then create the massive interest anymore.
But as I've said. The Europa League has problems through whole Europe. The decisive round of 16 match between Inter Milan and Tottenham in February barely drew 18 000 people to the stands. That would have been 70 000+ if the competition was Champions League.
Champions League matches was always sold out on Lerkendal. And the qualifying matches usually drew 10 000+ to the stands. Back in 2007 there was 14 123 spectators against Finish team Tampere United even after winning 3-0 in the first leg in Finland.