Lately, I've realized that most of the players in my D&D 5e custom story group that I am the DM of are not as engaged as they could be in the game. When I ask them how each really wants to play the game (LARPing, the usage of maps, NPC interaction, etc.), and what rules we should use (by the book, DM/player discussion), they answer "I don't know". They've been in this for two years, so I know it isn't true. They're just not putting a whole lot of thought into the matter. It's not their fault, either; I'm just not asking the right questions, and I'm not sure which ones should be asked.
So, the problem boils down to this: I don't know what's the best playstyle for them, and they don't either, so I need some more experienced players advice and suggestions. I ask you: What are the big questions I should ask them to help find out their preferred way to play?