They can be, but they will require far more labor to produce many of the same goods as one where workers are able to say "OK, we need 1 billion tons of cement to make 10 bln tons of concrete to make 20 million homes, that requires 10,000 concrete plants near where we're going to be using it, workers trained in x y z, 20 bln tons limestone, etc etc etc".

The scale of modern industry is bigger than individual communities.

Centralization of the basic industies enables any level of decentralization for downstream industries; your local pizza shop, whether run by a workers coop or a Small Business Tyrant, isn't signing multinational agreements to get flour or parts for the oven.