Please suggest a better resolution. What can I do ?

Absolutely agree with Nancy and Georges. The community of contributors is growing. So it is normal that the requirements increase. The images lack cotraste, it would perhaps also straighten the perspectives. In my opinion, a buyer interested in this monument will want either an "architect's" photo in which case the details and perspectives have to be worked on, or a "tourist" photo and in this case to make the images more alive, it is not a dead nature 🙂

The truth is, we will never know the exact thoughts of the Adobe Stock Reviewers.  @Nancy OShea is right, that photographers and equipment are getting better all the time and pushing the bar higher for quality.  I have photos in my portfolio that I don't think would be accepted today.

I can confirm that the four photos you posted have quality issues.  At 100% view the details are soft on all four photos.  There are blown out highlights.  And they would benefit from geometric corrections.  I also didn't find the light very pleasing to the eye.  I hope this at least helps confirm the rejection weren't without basis.  Don't let that discourage you though!  I like to turn rejections into opportunities for learning.

I genuinely wish you good luck!

The purple lens flare is a defect and not accepted on technical grounds.  I defer to Adobe Stock Contributor User Guide below.

https://helpx.adobe.com/stock/contributor/help/photography-illustrations.html

Some older images were grandfathered in from Fotolia, before Adobe Stock acquired them.

Photographers and equipment are improving each year.  Also there are more Contributors today than there were 5 years ago.  The competition is stronger and the standards bar keeps rising. That's to be expected.

Examine all images at 100-300% magnification.  Repair all defects if you can in Photoshop or Lightroom.  Discard the images you cannot repair.  Submit only your finest work to Stock.