You're asking a very complex question. This question can not be answered with a reason or two. There are many factors in play. Maybe Bitcoin is still too complex for some people. Besides, the majority are ignorant and closed-minded (change is hard to accept).
Current trend is still towards getting their stash and hoarding, so obviously you don't see people using it to buy any tangible items, which also mainly because there's not many of these shops around which will allow you to buy with bitcoin but not fiat. Getting paid in btc is also another reason as there is not many companies that are actually doing it.