What is the quality issue with these photos ? Can someone help ?

I agree with the other comments posted here. There is no sales potential for noisy, unfocused images - of any subject. Keep in mind that Adobe Stock databases already contain 11.6 million sunset images. Yours would have to be unique and technically perfect to be accepted or ever sold. 

The histogram from "Comet" shows clearly an ill exposed image with both, the blacks (and shadows) and the whites missing.

In addition, despite you having posted PNG files (why?), it is full of artefacts:

Night sky, as well as comet has this dark blobs in the image.

and compression artefacts on a PNG file should not be…

The histogram shows a highly underexposed picture.

Your last picture is as bad as the first two:

Oh, and by the way I'd be very proud if I'd managed to photograph a comet. It's a great memory, but it isn't world class stock photography.

Hello,

Sorry, but these photos are not that good, will definitely not meet Adobe's quality standards!

Focus, exposure, composition... quite a lot really😒

Have a read of this from Adobe about how to create better photos to get you started!
https://helpx.adobe.com/stock/how-to/tips-stock-image-acceptance.html?set=stock--fundamentals--adobe-stock-contributor

Contributor handbook
https://stock.adobe.com/pages/artisthub/pdf/contributor-handbook-2022.pdf

First of all, your signature is not allowed. Your photos show no specific subject. The comet, for insrtance, is way to small. The exposure are also off.