It's to make it easy for your readers to keep track of where they are. Each chapter is meant to be readable in a couple minutes while the reader is between tasks, then the app saves their place for them. If they're longer, you end up with situations where the reader is interrupted when they're not done reading the chapter, and the app isn't going to remember that they were on line 132 of 209 or whatever. They'll have to find it themselves, which is a hassle, which creates a barrier for them returning, which is bad for business (both yours and Tapas).
Personally my novel chapters (unpublished, I'm working on the buffer) are ~10,000 words long. Obviously too long for a single entry. So for me each tapas "chapter" is just a single scene of what I consider to be a chapter, like "Episode 1, part 1" etc. Not that hard. If the reader keeps reading because they have extra time, it's as natural as scene breaks in a regular chapter, and if they need to go do something else, it won't feel weird because the transition was between sets, like in theatre.