How come there's not vanilla bars like there are for chocolate?

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

For a moment I thought you meant "bar" as in a place/business. I nearly searched for chocolate bars in my area. :)

Chocolate bar is mainly made from cacao bean, which after processed into cocoa butter and cocoa mass, then add together with some other ingredient to get chocolate, so the main ingredient is still mostly from the same raw ingredient. Compared to vanilla(extract), which is made from vanilla bean, is a flavouring that's only meant to enhance the taste of something. So you can have vanilla bar but it will still made from something else as the main building structure of said bar, but with vanilla flavour.

You can dip things in chocolate. Vanilla doesn’t work well as a coating; it’s more of a flavoring.

That’s why there are candy bars and yogurt bars as well… and peanut butter bars.

We don't see vanilla bars as often as chocolate bars because of how we experience flavor and pleasure. Chocolate has compounds like theobromine and caffeine, which give it a mild stimulating effect, making it feel more exciting and energizing. Plus, its rich, complex flavor profile appeals to a wider range of tastes. Vanilla, on the other hand, is more subtle and lacks the same sensory punch, even though it’s a universally loved flavor.

https://www.amazon.com/s?k=vanilla+bar&ref=nb_ss_gw

There are various vanilla-flavored bars.