Apologies for the length
Je n’ai fait celle-ci plus longue que parce que je n’ai pas eu le loisir de la faire plus courte.
I would have written a shorter letter, but I did not have the time.
(literally: I made this [letter] very long, because I did not have the leisure to make it shorter.)
Unfortunately, this is how I tend to feel about most things I write or pretty much every talk I give.