As with anything it comes down to the quality of it, there are films where dialogue scenes can be boring as they are just aren't well written. Even worse there are films that set out to be dialogue driven that are badly written so you do finish the movie with the view that 'nothing happened' because the dialogue was so poor that ultimatly nothing did.
Two of my favourite films are Before Sunrise and its sequel Before Sunset but these movies are just two people walking around talking so most people I recommend them to find them boring.
Now I don't think it in most cases it has anything to do with them being too stupid but it seems more to do with people not having the attention span to listen to dialogue. Its much easier for them to appreciate explosions or simply setup/punchline jokes found in rather poor films like Transformers or Valentines day over movies like Clerks, Before Sunrise/sunset, Social Network and the likes which are all about the dialogue.
Tarantino mind you is someone who seems to get away with pleasing both sides as there is enough action and gore for people who don't have the attention span for dialogue to still enjoy