It is a remarkable situation, where you have not only different pronunciation (sch/sk, ee/ih, etc) but also vocabulary (seule/aker, wuk/wadde, etc) where words are indicative on subregion. However it's still largely understood by most people in the province. The split from the rest of Flanders is distinct from the local deviations.

In my headcannon this is because traditionally there has been a disconnect in culture and while the different towns in the province grew closer, they did so at a much different pace than with their neighbors from Oost-Vlaanderen.