A good bone broth doesn't taste like bones per se, at least not exclusively; it tastes like the meat of the animal whose bones it's made from. However, the majority of meaty flavors don't per se come from meat either; they come from the complex Maillard reactions that occur when meat is cooked and the meat proteins and reducing sugars react. This is as true for the meaty flavors of good bone broths as for the meaty flavors of meat itself. Thus, no matter how the chefs may have described it, the overall preparation of a bone broth doesn't merely "extract" pre-existing flavors: it literally creates the compounds responsible for the flavors we love (via roasting), and only then extracts them via the simmering/boiling process.
Now that said, a bone broth will have flavors that aren't identical to a meat broth. Bone broth is (understandably) especially known for being higher in mineral content than meat broths. But bone broth shouldn't be "plain"; that's a sign that something went wrong.
Speaking of that, in addition to not roasting them, you did likely also undercook your bones. When I make bone broth, I usually let mine simmer at least overnight in my crock pot (a bowl of warm chicken bone broth in the morning does the heart good) or sometimes longer (if I'm making chili, I'll let it go as long as two days, long enough that I have to add water partway to prevent it burning dry). I've read online that it should be about 12 hours for a poultry broth and 24 for a beef/redmeat broth, but in my experience, you shouldn't be afraid to let it go longer even than that; the longer you simmer it, the longer you let the minerals leach out into the broth.