They could be oneday, look at Forest.
Yeah, coz football was the same back then wasn't it? Arf.
Forest were stuffed by their lack of money, pure and simple. They are a small club in revenue terms and capacity terms (20K odd). The only reason they won their European Cups was because of Clough and the players he managed to attract because of his stature in a time gone by were money wasn't one of the primary motivators of these primadonnas we call footballers these days.
Unfortunately he lost the plot near the end and they were relegated even with players like Pearce and Keane and he couldn't survive in a changing world of football where money talks so he resigned. Not to mention taking into account his failing health.
Once they were relegated there was no way back to the big time because they didn't have the funds or the ability to attract another top class manager and hence top class players.
The same is never going to happen to the big four. The most vulnerable are Arsenal because they are not current bankrolled by a billionaire. Man United have massive leveraged debt but they are still the biggest revenue earning club in the world, so they always have money available.
Football, these days, is literally ALL about the money. Fat cash means world class managers and that plus cash means world class players will follow.
/sigh