Printing is a good constraint against getting too long, both the physical and cost constraints. Though the Harry Potter series in full still managed to reach a million words.

For another comparison, the Bible is around three quarters of a million words, and tends to use special paper (20–40gsm/30–50 micron) so it works in one volume.

Handwriting is also a good idea for encouraging keeping lengths down; typing and dictation make verbosity too easy; and as for LLMs, words are clearly far too cheap there.

There is a lot of web fiction out there that would be better if the authors had written "the end" a few years ago.