It's up to the fansite admin to start the process of creating the fansite item. This is usually, but not necessarily, a contest. It's not mandatory though and the fansite may wish not to have an item at all. TibiaMaps, for example, only created its item in 2021 even though it was in the program since 2016.
I can't tell specifically about the reasons behind TibiaFanart's decision, but it could be just that they are waiting to start the process. Considering the fansite theme, however, I assume they'll eventually get their item and put a lot of effort into it, however they decide to proceed.