There are different kinds of game abandonment which you may wish to familiarise yourself with: https://support.chess.com/article/338-how-does-game-abandonment-work . I.e., whether the timer has to rundown depends on certain conditions being met.
That being said, not all disconnects are intentional. Sometimes one's internet just doesn't hold together, or one must suddenly stop playing and attend to something else (like appearing to be working and not playing chess).
Also, while you may consider their behaviour annoying, and doing the right thing in reporting them, there will never be a shortage of such people whether bans occur or not. That is the unfortunate reality of all kinds of undesirable behaviour on this and other public sites.
I am relatively new to Chess.com. I find it very annoying that quite often when I am in a favourable position my opponent will disconnect. This doesn't cause the timer to run down but disconnects within seconds which I suppose should be in my favour. However, this is clearly to avoid having to resign and I find this very disrespectful and unsportsmanlike and therefore rather annoying. I have looked at several forum topics and they almost all say that this is not possible and that the timer must run down but this is not the case. I report every incident of this for stalling./quitting. Can anyone confirm if any action is actually taken against these players when this is reported?