Well a sure fire way to kill any action adventure franchise that needs young fans to keep it alive as older ones phase out is take it away from kids for years. No viable toys, clothes or merchandise, kid centered TV... I mean what else would happen?
I wouldnt go as far as saying it was taken away, it just wasnt marketable in the face of competition. There was an X-Men cartoon 8-9 years ago, but was cancelled. Movies mismanaged and poorly directed doesnt help either.
But the X-men have been visible in media. They have been playable characters in every relevant marvel video game to this day, plus action figures by Hasbro. I play Marvel Contest of Champions, one of the most successful mobile games on the market right now, and there has never been a shortage of X-Men in the game.
Edit: just wanted to add, the only video game in recent history, Marvel vs Capcom Infinity released last year, tanked because the developers didnt listen to the fans and refused to add X-Men characters to the game. It tanked so bad that it has already been abandoned by Capcom. Rumor is the game will be rebranded and relaunched with the X-Men included.