Your'e right Csilla, but this is where I find Duolingo frustrating. On some occassions like this, the literal translation is required and we are penalised for offering something which sounds less akward, has exactly the same meaning but it is obviously not a word-for-word translation. Other times the reverse is true. Grrrrrrr.
Duolingo's focus is on grammar. There are many things one might say. Here it is simply: These decisions are good (not "these are good decisions"). Yes, they mean the same thing. But the exercise is to be translated as is unless there is a good reason not to. It is grammatical, correct and natural. Your sentence is good, but it is not the translation. In the past, there were some sentences that had more than 3,000 different variations in English. I don't think anybody really wants that. Once you have completed the French tree and mastered what it can teach you, feel free to spread your wings and launch into new areas. There is a wealth of material out there to study and practice on.
But what constitutes "... a good reason not to"? In another exercise I translated "J'ai besoin de ..." as "I have need of .." because it is the literal translation and is grammatical correct - albeit it old fashioned - but it was marked incorrect. As I said previously, consistency is key. Notwithstanding this gripe, Duolingo is a cracking app.
We have put a lot of work into improving things over the past several years. I think it is obvious for those who have been around a while. There is still much to do and nobody is perfect. We keep trying. As to "avoir besoin de", you no doubt read that it is defined as "to need". So even though the very literal translation is "to have need of" does work, it is as you say, a bit old fashioned. Duo is trying to teach that expressions must be taken at their meaning and that literal translations sometimes work and sometimes they don't. By saying "have need of" is perfect, it perpetuates the notion that literal translations should always be accepted and that is just not the case.