"Decline" is an ugly word ( when it does not appear in proximity to "Alabama" ).

Every apex is followed by a decline, all of them. Term length is relative measure, we know this. What I'm saying is: we're still very close to a long term apex, which we should recognize and enjoy.

Also, there's are different kinds of popularity. There's broad, shallow appeal and there is the mature, passed-the-test-of-time wonders that remain attractive after the initial infatuation, novelty period wares off. AKA: a classic.

Our national game of football is so damned amazing, that its infancy, formative period is still ongoing. Medieval Mob Football happened for centuries in Europe before centers of learning figured out how to adapt it into smaller, more manageable games.

Overall, Mithridates, you are correct. Some level of decline is inevitable, especially when there's been so much growth, so quickly! Rock & Roll was everything, until it wasn't. It didn't die, the pop-culture crowd just moved on to the next thing to explore, but the music is still made and people still enjoy it. Our football may shed a few fans who were really a better fit for a different game, but it ain't dying anytime soon.