Superficial Conversation

I've been "friends" with a Swiss couple (from a German canton) for about two years. I'm based in a different country but we're in fairly regular contact, have stayed at each others' homes during holidays, etc. Despite being very friendly, hospitable, and generous, I just find that they seem to be unwilling/unable to talk about anything substantial. Conversation is limited to superficial topics like food, travelling, hobbies, etc. I'm running out of steam, since I feel that there is no potential for really getting to know them, or vice versa. What's the point of being "friends" if you can't talk about things that actually matter to you as a human – your worldview, your opinions, your struggles, your desires and fears? I've tried to introduce "deeper" topics many times to no avail. I understand that Swiss people are "private," but genuinely: do friendships ever evolve beyond this? Am I missing something?