I have visited few author's profile to see their variety of stories that they have posted here, and noticed that many drop their stories in its beginning phase, like one or two chapters and bam! dropped. I can think of a few reasons like not having time or loosing all interest after writing couple of chapters but are there more reasons?
A variety of reasons. Writing a novel is like being in a romantic relationship. A lot of them don't work out for all sorts of reasons. It's pretty uncommon for someone to end up with their first love or get into a long-term relationship on the very first date right?
Sometimes they are deal-breaker reasons like the story is just a train wreck and it's easier to start with something new. Or you're unlucky and come across a toxic troll right at the beginning who criticizes every word and/or 1-star rates your work without really reading it. Maybe they'll stunt your novel's visibility by chasing away potential readers that way, etc. Other times you drift away from writing and don't have the time/capacity to rekindle that initial motivation.
A lot of us here are amateur writers. We might improve in great strides as we start to write regularly. At some point, we may realize that the initial novel we were writing no longer represents our skill and no longer satisfies us.
Personally, as a writer, I want to be very satisfied with anything I publish. I am unlikely to stop my novel at this time because I am still very happy with where it's going. At the same time, it's a double-edged sword because my updates are slow as a result of so much editing/planning hahaha. So I have to actively motivate and inspire myself to keep writing in between publishing chapters. Long-term projects almost never run on just the initial passion that a lot of people start writing stories with. That fizzles out quickly as you pass a certain word count. It takes discipline and effort to recognize when you're losing motivation. You will need to plan it out and find ways to inspire yourself/keep going.
And as much as some people like to argue it's all down to hard work and powering through to do well, sometimes it's just plain damn luck. Things worked out because it happened to be the right time and right place for your novel to publish. And that's fine too. Luck is also a part of success.