Take Jabba the Hutt for example. He can understand basic just fine, and he could probably speak it if he wanted to. He just prefers not to. Why? Because it is a manifestation of his power. He thinks of Huttese as a "better" language than basic, putting himself above those he interacts with. His use of a translator is pure self-indulgence; something to display his wealth and hedonism. This is a facet of Hutt culture. The Hutts believe themselves to be a superior race, and often do hold more power, as is seen in various examples such as Jabba, Gardulla, Aarba, etc.
Similarly, the Mandalorians think of themselves as better than other cultures. They refer to themselves as Mando'ade (Children of Mandalore), and everyone else as aruetiise (outsiders). Mandalorians have such a rich identity; they are defined by how well they maintain their culture. One of the resol nare (six actions) is to speak Mando'a. This is similar to how there are language laws in Quebec to maintain the French language. The Quebecois are incredibly passionate about keeping English influences from taking over the province, which must be extremely difficult for them being a part of a primarily Anglophone country. They have laws for building signage, radio and television programming, and even customer service saying both "Hello," and "Bonjour." I think they do a fine job of maintaining their culture, and despite their repeated attempts at separatism, value the inclusion of Quebec as a part of Canada.