CS paper rejected for lack of technical contribution; what does this mean, and how can I fix it?
Since you ask those questions, I assume you are relatively new to CS research. I do not know if you have previous research experience in any other scientific area, but let's assume you are new to research all together. Correct me if I am wrong.

When your paper gets rejected, the feeling of rejection sucks. It sucks a lot. But in research you have to deal with this rejection and move-on. It does not matter if other people's works that you consider worse have been accepted. Maybe they are better than yours maybe not. But that is really irrelevant. Focus on your work and how to improve it. 

The questions you should be asking:


Is this problem you are trying to solve interesting? 
Is your solution substantially better than previous state-of-the-art? 
Are you certain that you described related and recent literature thoroughly? Are you up-to-date on related literature?
Did you make clear the benefits on your approach? 
Is your paper well presented  and written? Have you explained your approach thoroughly (with pseudocode, figures) and not just with words?
Were your experiments thorough? Did you use many datasets for your experiments? Have you used the datasets that the related papers use or at least similar if not bigger in size and scope? Have you compared your results with previous approaches? Have you many charts demonstrating the various aspects of your solution?
Have you advertised your work by finding many test-cases for your problem? 


If any of those answer is NO, then you must turn them to YES, before resubmitting your work. You must understand that if your paper or the problem you try to solve is boring, then it gets rejected. It is as simple as that. In that cases, the most usual reason for rejection is "not enough contribution". So, probably it is also your presentation that needs to be fixed.

Also, it seems rather strange that although you are probably new to research, you have submitted two papers at the same time. Perhaps this is too ambitious and it would be better to focus on one of them, improve it and resubmit it. Perhaps, they should be sent to different venues that are more tailored for each one of them. 

And last but not least. Do not worry. It gets better with time. Both the way you handle rejection and the way you write papers. So, improve what needs to be fixed and everything will work out.