There kinda are.

But the reason is that chocolate has cocoa butter, and vanilla doesn't.

You can make an entire bar of chocolate, with nothing but chocolate (though it would be a different kind of taste and texture than you'd expect, probably).

Vanilla can be made into a paste, and that's as solid as it gets by itself.

It's alll about those fats that crystalize. It's why chocolate can be tempered, which is how it can be made into bars that hold their shape well.

Now, that's perhaps a little over simplified, but it's the answer.

There are confections in bar shape that are vanilla flavored for sure, but they aren't vanilla bars in the same way a chocolate bar is a chocolate bar.

It doesn't help that real vanilla has poor heat tolerance which is not great when being used in candies and desserts. It's part of why you'll usually see vanillin used instead; it gets close enough and doesn't suffer as much from being heated. It's also much cheaper, so any loss from heating is no big deal in comparison, so they'll just add more to make up the difference