I don't have time to read your petition; but quickly here is a guideline.
First, you should avoid saying the same thing in other words.
Second, prioritize. For each thing you are talking about, figure out what will be most important to a new reader, and talk about that. In the high-priced consulting world, they stick very closely to the Rule of Three, applied recursively: You should pick at most three topics to speak on. For each topic, you need to find the three most important points to discuss.
Third: Your petition is a kind of sales document; you are trying to sell a position. Thus, try to make every sentence personal for the reader: It feels weird, but it works: Do not go more than one sentence without a pronoun referring to the reader or clearly instructing the reader. If you can find a way to do that, this is what keeps people reading, they love to read about themselves.
Fourth: Question the need to be concise. Getting your point across quickly does NOT increase sales (signatures on your petition). The best selling ads and sales letters are long! There is actually maxim in sales writing; "The More You Tell, The More You Sell". (As long as you do it without repetition or descending into trivia that does not matter and will bore your reader).
It is true that a very large percentage of people reading your sales letter may decline, but the rate of that is not linked strongly to the length. The rate is linked to whether the product appeals to them. For those people, the more informed they become about the product (for example whatever your petition hopes to accomplish) the more likely they are to buy it. This is why a long form works; a short form leaves them with unanswered questions that are large enough to not risk the buying action (signing your petition).
Trying to get your point across quickly in a few words is a rookie mistake. It can help get people to start reading; but if all you have given them is a few words, you haven't given them enough information to persuade them they should take a chance on you.
So think of the three biggest benefits the proposed action from your petition will deliver to the type of person you want to sign it. Then detail them in order. You can allude to more in a paragraph, but try to close the argument after three, and finish with asking them to sign and help you move the project forward.