I think there's a problem related to what Rolf is asking about that needs our best response. Here's an effort to describe that problem and give a provisional answer:
"If it's so easy, Epicurus, to caricature your philosophy to make it seem like the opposite of pleasure, don't you think you have a problem with the way you're saying it?"
There's a section of Frances Wright's chapter ten, especially the part I underlined below, that makes a similar point, where she has Epicurus say:
“Zeno, in his present speech, has rested much of the truth of his system on its expediency; I, therefore, shall do the same by mine. The door to my gardens is ever open, and my books are in the hands of the public; to enter, therefore, here, into the detail or the expounding of the principles of my philosophy, were equally out of place and out of season. ‘Tell us not that that is right which admits of evil construction; that that is virtue which leaves an open gate to vice.’ This is the thrust which Zeno now makes at Epicurus; and did it hit, I grant it were a mortal one. From the flavour, we pronounce of the fruit; from the beauty and the fragrance, of the flower; and in a system of morals, or of philosophy, or of whatever else, what tends to produce good we pronounce to be good, what to produce evil, we pronounce to be evil."
I think part of the answer to this question would include referring to VS29. (Bailey) “In investigating nature I would prefer to speak openly and like an oracle to give answers serviceable to all mankind, even though no one should understand me, rather than to conform to popular opinions and so win the praise freely scattered by the mob.”
I don't think Epicurus expected that his letter to Menoeceus would survive isolated from his other ethical works on the End, and his works on the Canon and On Nature and so forth. When he wanted to distill his ethical philosophy down to its core essence, he chose to include in PD03 the key fundamental point which is not stated so bluntly in the Letter to Menoecus: PD03. The limit of quantity in pleasures is the removal of all that is painful. Wherever pleasure is present, as long as it is there, there is neither pain of body, nor of mind, nor of both at once.
If the Principal Doctrines had survived and the Letter to Menoeceus had not, I don't think we'd be in nearly the same situation we are now. We'd still have knowledge that absence of pain is a crucial concept, but we wouldn't be dealing with the confusion caused by saying in isolation that when all pain is gone we have no need for pleasure. That statement makes sense only when you realize that it means that we have no further need for more pleasure because our experience is already full of pleasures. We haven't gotten rid of pleasure along with pain, we'll filled our experience with all our own personal combination of those mental and physical experiences that everyone recognizes as pleasure, along with those other experiences of health and stability that everyone doesn't but should also recognize as pleasure.
If you keep PD03 firmly in mind as the starting point, and you realize that it's being stated as the third most important thing to know in the whole philosophy, more important even than a statement that Pleasure is the goal of life, it's easier to see that there's something special about this formulation which has to be treated like an axiom never to be contradicted. With PD03 in mind you know that pleasure and pain cannot coexist in the same space, and that no more pleasure can be added when all pain has been removed.
And if you know anything about the major philosophical debates of the age, you know that this addresses the major objection to holding Pleasure to be the greatest good that had been stated by the opposing philosophers: that pleasure can always be made better by adding more, and that therefore pleasure can never be properly viewed as full or complete. You don't need to be told that Pleasure is desirable, because no one in their right mind would assert that (even though the Stoics and others moved in that direction). What you needed most of all to be told is that there is an answer to the anti-Pleasure logic problem, and that the answer to the logic problem is that Pleasure when viewed as "Absence of Pain" cannot be improved - there is no "better" than can be reached by adding more pleasure when your experience is already completely full of pleasure because you have removed all non-pleasurable experiences.
This is the key philosophical answer which Epicurus' formulations was targeted at explaining. Epicurus was aware that he could and would be misconstrued and misrepresented, but he also knew that nothing will satisfy that type of person. The most important thing was to provide the key for those who are capable of figuring the problem out. No doubt in other places he did explain the issues in more plain and simple terms, but it appears confusing to us because from Epicurus' own hands only one letter on ethics and a list of key doctrines survives.
That's one way I would begin to answer someone who legitimately asks Why didn't he state this more clearly and why does this have to be so confusing?