Kale vs Broccoli

I had some Broccoli and some Kale growing outside, I noticed something interesting. They both have green leaves, somewhat tough, and a flowering head that is the traditional storebought "broccoli" look, somewhat. In fact they are closely related Brassicas.

Why is it that Broccoli is sold in the stores with the flower heads pre flowering, while Kale is sold by the leaf?
Maybe it is where I live but I don't recall seeing broccoli-leaf crisps like they always have in health food stores with Kale leaves.
From what I read online they have different nutrient profiles, but they are similar in taste when stir fried together.

I think it's because those two particular brassicas were selectively bred to have better flower heads or leaves.  You can eat those parts from any of the brassicas but they probably taste a bit better or are more palatable from the intended one.  Plus broccoli and cauliflower are the only brassicas I'm aware of that flower in the first year instead of as a biennial.  So that's a limiter to growing flower buds from other members of the species.

Luke Bryan wrote:
Why is it that Broccoli is sold in the stores with the flower heads pre flowering, while Kale is sold by the leaf?
.....

To me, broccoli tastes quite different from kale and I actually prefer the taste of broccoli leaves over that of kale leaves.  Nevertheless, leafy kale is one Brassica culinary selection over the centuries and broccoli is another, being cultivated for the floral head.   In our northern midwest USA region, most kale gets quite bitter in the summer heat.  A friend from Brazil suggested trying 'Portuguese Kale', which I was able to find through one of the major seed sellers online.  He claimed that in summer in Brazil, where it gets quite hot, this kale variety maintained a good flavor and tenderness to the leaves.....perhaps more like broccoli leaves to me.  I will try to find out this summer if that is the case.

We eat the flowers from the kale but they are a lot tinier than broccoli. On the other hand they are quite abundant. I bet they wouldn't travel very well or last very long compared to a broccoli head. Kale seed pods (immature ones) are SOOOOO yummy. I don't think I've ever seen or heard of those being sold or served anywhere except my own garden.

Broccoli leaves to me are much tougher than kale. But they are completely palatable if you are cooking them or chop them up. For selling, a broccoli plant doesn't have as many leaves as a kale plant.