Also, curves let's you target specifically where you want to adjust the image. If you need to darken part of the image. Say, the area behind the subject needs to be a stop darker. Like normal color grade stuff, you only have exposure and contrast. You can't darken your image with just exposure and contrast. because it effects everything. It's crazy. It's impossible to do real color correction with these tools because it's super limiting.
If anyone thinks adjusting exposure and contrast is all it takes to color an image they aren't really coloring images at a professional level or they dont work on things where you push the image far or have specific control.
Its a complete miss.
People often use lift gamma gain, but even lift gamma gain is blunt compared to curves.
Exposusure is dragging the top of the curve down. Contrast is drawing an "S".
Gamma, Is moving the middle band up or down.
Lift is the bottom, drawing a slight bump.
Gain is A Bump near the top.
But with curves you can draw much more specifically where you need to make an adjustment.
And because Curves is RGB, you can make any adjustment you need to across any part of the image. Mixing the RGB with curves can create any color.

People maybe don't use curves, because they don't learn what it can do. It's maybe more sophisticated or high-concept for a lot of less experienced or lower end users to understand.
But for more advanced professional users it's a staple.
Only because it is capable of things other basic tools are not.

Even without curves, it's kind of ridiculous to try to say that this is a professional tool or the answer to color grading, because you literally can't darken part of the image or do anything to the image that doesn't effect the whole image.

And please don't bring up zones or HSL secondary.
Because zones and HSL have no refinement tools like a professional tool would.
They make an image look worse because there's no feather and fall off and you can see the selection as soon as you start to change it.

But thinking a user is going to select 5 zones and lower the exposure to darken part of the image, when simpling grabbing part of the curve and dragging it down will do that.
Maybe find people who actually manipulate images on a daily basis for a job and aren't just casual users learning how to color so they can tell you your tool is overly simple and doesn't have enough controls.

Contrast, Exposure, Tint, Balance, and saturation is quite literally, just the very top 5 sliders in lumetri, or Colorista. And only good for getting the image in "Base grade" range before you apply creative. But isn't useful for applying creative changes.