The problemset is persistent and some ranks are affected by number of solved problems. If the solutions are published it would be to easy to just copy the solution and submit it. Hence they will not be published. Authors are also requested not to publish their exact code. It is better and maybe more beneficial for everybody to discuss ideas and algorithms of solutions.

The code is visible to admins and the problem setter of the task he stated.

For some of the problems taken from competitions around the world it is probable that you may find a coded solutionon some other site. It is encouraged though that you understand the algorithm and code it yourself.
kfas

Would it be possible to allow each person who solved a particular problem to see author's solution for it? That shouldn't have any effect on rankings, because people won't gain score by using author's solution.
I often like to see how other people implement their solution so that I can find solutions that are shorter,easier to implement and that have less special cases.

It might change the time / memory ranking.

How about opening a special forum for available for those people who have solved a particular problem. So that people would be describe type of solution which that had implemented. Posting code would be disallowed.