That's because if we start and stop with that letter we are taking Epicurus' words out of context, and not accounting for the circumstance that Epicurus was writing for students who wanted summaries to make things easier to remember, but who were otherwise very familiar and had intimate access to his full views.
That's one reason I wrote My translation and commentary of that letter, to provide some context, both historically and philosophically. I need to give that a thorough reread and maybe do an updated edition. It's been a few years now.