Food is highly cultural and habitual. Changing their diet can take years for some people. Also, many people probably never have tried many truly vegetarian dishes, so there is a learning curve.
I for one really gained an appreciation for curry, and since they're stewed to fuck anyway you barely notice whether or not there's meat in them.
I hope that people trying to improve their diets will discover spices beyond salt, pepper and chillies, lol.
I do believe part of it is that western diets are more about the ingredients and the textures / mouthfeels / flavors thereof than spices. Which is ironic, given the whole colonization and world spice trade thing from some time ago.
