i dont really know how important it is...
for example Cardano never had ANN thread and still its very successful
so thats not on the top of the important things to do when you open a startup.
This is important in terms of community communication here in the forum and of course to give all the details from your project social links etc . even ETh has announcement thread here .
maybe cardanao believe that they have enough investors so it would not be a problem for them if they dont create one.
but for new project this should be one created here and of course other people here individually can review your project .