"I didn't have time to write a short letter, so I wrote a long one instead."
That quote captures an essence of writing. In a shorter piece, every word does more work. There's nowhere for junk to hide. You can't cover up or caveat-away bad points.
Rambling is easier than succinctness. If you ramble on for long enough, eventually people get your drift.
But you waste people's time.
I should work on this.