I drop things when I just stop working on them.
I do have reasons that I stopped working on it,
I had an older comic I ended like 4 years ago. It ended because I didn't have time to work on it during that first semester of college. I chose to not come back to it, because when I had time again I had other things I wanted to do that were better planned. The old comic was meant to be story driven but I didn't plan anything ahead really, down to having no buffer of pages finished or even anything written past the next few pages.
Basically I had to go on a hiatus because I couldn't work on it, then by the time I had time to work on it I released it was honestly really bad. It was a learning experience as the new comic has been in plans basically since that other one stopped 4 years ago, and I'm barely releasing it now, I've got months of finished pages for buffer, based on my release schedule I've got a whole years worth of detailed script written, and summaries of the story events to happen after that so I'm fairly well prepared and my story will be a lot better because it's planned.
Then again it could just be a long hiatus, I have a non-comic project that I've worked on off and on for the last few years where I'll go months at a time not doing anything only to work on it for a week or 2 straight for a while, then stop again.