Because the files already looked fine for the most part. Assuming the JPEG is sensibly encoded the human eye probably won't be able to detect the quality improvements in a different algorithm.

So the only place they can target is where JPEG starts to break down: When you've cranked the quality knob down to 20 and you're seeing macroblocks and other artifacts in the image. But this is a niche use case as network speeds continue to improve every year.

The worst part is that they have to compete with free, and that's never easy, especially if you're talking about "well, it's still distorted, but the distortion is less displeasing to the eye", also you need to configure some pain in the ass licensing system and work out how to do the payments.

> people insist on the same quality with lesser size.

Because a great proportion of people browsing the web have slow connections and/or data caps.

> How about more quality and the same filesize?

We're already able to get acceptable quality.

If you can get one then you can get the other, for any compression format that allows varying compression ratios.

Part of it is about quality. These new formats now support 10+ bit color depth (which is critical for modern displays and for HDR) and full 4:4:4 chroma subsampling (to preserve pixel-level as needed). Many apps/services are currently evaluating or already migrating to AVIF or HEIC because these formats unlock those improvements in image quality, even without a major reduction in file size.

PNG already exists.

The answer is simple: money