Atletico madrid is still on their capacity to "exist", not on "win" the champion league. Diego simeone, as atletico madrid's coach never had a great expectation for his club in UCL; therefore, even though they were not favorite to do this, atletico madrid still has little opportunity to win UCL.
Although the officials of Atletico madrid were always improving their teams, their efforts were pointless since the gamplay and strategy of the simeone remain the same. When atletico madrid advanced to any level in the champion league, such quarter or semi finals, ATM officials feel good enough.
With the present team, Atletico Madrid lacks capacity to win the UCL. Atletico madrid made it to final at 15/16, really lucky. So in essence, all things considered, it makes little difference how much atletico madrid improves; uninspiring strategy and gameplay by Simeone will prevent them from winning UCL.
What you say is true, I also pay attention to Atletico Madrid every time they enter the UCL and being able to reach the quarter finals is nothing surprising anymore. Their performance remains like that, the same and no different from the previous season. It's as if Simeone hasn't developed this club well, the strategy is monotonous, while in terms of player capacity more or less changing with new ones, the level of effectiveness is still not increasing sharply. Atletico Madrid seems to be stagnant or really needs a new coach who has different ambitions and ideas from Simeone. Honestly if Atletico Madrid wants to appear to be developing, maybe it's time to think about a new, more modern manager with a variety of strategies.
Domestic clubs especially rivals Madrid, continue to develop, Barcelona is also trying to cover all its shortcomings, even with limited players and limited funds, but there are always different things every season and with the arrival of Girona they also starting to be considered worthy competitors next season. Therefore if Atletico Madrid does not upgrade its players and coaches next season this club could be left behind by its rivals.