Usually journals takes longer time and it is difficult to publish over there. Many journals don't have Impact Factors, so there reputation is again an issue.
In some areas of computer sciences to publish in top contents is as hard as publish in top journal. Actually it might be easier to publish in journals instearad of top conferences. Conferences are for dissemination of ideas, thus papers presenting some novel ideas can be published even if the technical details still need some polishing. On the other hand, journals are for consolidated work. Also journal publications can go through several rounds of reviews (which take time).
Dear Dr. Qaim Mehdi Rizvi, Conferences are platforms for presenting an idea but not a complete solution. When you are publishing in journal then you have to demonstrate the implementation process, analysis and impact and therefore, its a little difficult to publish in a reputed Int'l journal.
Thanks Afaq sir, you are right. Because in some cases journal committee return papers just because of it is not fully related to their theme or specialization. Again thanks for your guidance.