true the harem part could be one reason, but that is not always the only one. it could be the art style, certain elements of the story, advertisement, etc. although most people are into harems, imo they are mostly into that because it offers most content in one playthrough. multiple ending games for example although popular depending on story, are not THAT popular because not everyone has the time to go through the same game multiple times to see a few renders more. plus in most harems nowdays, you can pretty much have a multiple ending for those ( still trying to figure out why) who want solo endings and have the time to play 11 different versions of the same game/story ( yeah I still got nothing on this)
but at the end of the day, as long as you are good with what you create and it makes you feel ok, then its good, because most of the time, devs who like what they created, will commit to it and finish it.