Actually this isn't entirely true, considering Atletico and Dortmund are regulars in the quarter final stages these days - although the reason for this is, with the title race being a closed shop in their respective leagues, both of these clubs can go into the competition with a very important safety net: they know that, barring a catastrophic season such as the one Dortmund had a few years back, they are more than good enough to qualify for next season's competition via their domestic results, which allows them to balance domestic and CL football.
It's not a coincidence that you saw Premier League teams make the latter stages of the Champions League at the time where the Premier League's top four places were a closed shop, because the odds of those same four teams missing out on CL qualification the following season was minimal - but as soon as City were given the funds to compete the situation changed, as suddenly there were four places available for five teams, and that meant that teams who had spent years coasting their way into the Champions League suddenly those teams were now having to balance domestic and European football far more effectively, and things were already falling apart for some of those teams before Spurs had nudged themselves into the conversation.
Liverpool are the most obvious example of this, as their current pattern looks like this...
Season One: Qualify for the Champions League by finishing in the top four
Season Two: Finish outside the European places due to an inability to balance domestic and European football
Season Three: Without the additional European fixtures, focus on the league to qualify for the Champions League by finishing in the top four
Season Four: See Season Two
Season Five: See Season Three
Arsenal certainly look like they're falling into this rut too: the stage was set for them to potentially win the title last season as Chelsea, Man City, Liverpool and Man Utd all conspired to have poor seasons for various reasons, be it failing to balance domestic and European football, failing to see how unmotivated the players will be if you publicly tell the world that the manager'll be off at the end of the season no matter what or failing to have any reason to listen to the instructions from the gobshite in the dugout who bullied the club's medical staff out of the door, and yet they never came close to mounting a credible challenge - and with Chelsea and Liverpool recovering (as neither were burdened with European football) while Spurs and City remained consistent on last season, suddenly they find themselves staring into the abyss that is a glut of Thursday night matches in the far-flung wastes of European football.