Once I got past Gold and into Platinum, I started seeing some of this. There was a point where I was frustrated trying to fill my hero chests, it seemed to take forever. I briefly considered becoming a cup-dropper myself, just to face easier fights to fill my hero chests.
I ended up not doing it, instead I just kept building my team, and now I sit in Diamond and I revenge anyone who comes at me, and I find myself spending gems to reset my hero chest all the time, because I can fill them up much faster than I used to.
I can certainly understand why people do it - when you reach a point of frustration trying to fill up a chest, one might consider the alternatives available to them to make the game more fun for them. And if having easier fights is fun for them, well… that’s fine.
There is ONE THING that I dislike about cup-droppers, and that is: please, please, PLEASE put five heroes in your defense. The people who put up only 3 heroes, or 1 hero… that’s a waste of everyone’s time. At least give five weak targets so that the person attacking you (and helping you achieve your goal of lowering your cups, which ultimately helps you fill your hero chest) is also being helped with their own hero chest.